You were asking about how to promote, but I thought I'd address the structure of your offer if you don't mind. I'm not trying to sound like an a$$ if it comes across that way but just thought this might help.
First off, I'm not currently selling anything on Amazon, but as a marketer, put yourself in Amazon's shoes and your customer's shoes. Both of them are your audience You are selling to both your retailer and your reader just like any book publisher and distributor does. If you want the customer to buy, you need to make your stuff attractive to the customer. If you want Amazon to promote you and your work, you have to be attractive to Amazon.
I would think that you're probably losing a lot of possible sales with that cover. What can you tell me about the two books in the middle vs. the two books at the ends of picture below?
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The titles on the two center books can be read easily. If someone just goes explicitly looking for you or your book by title, they might buy the book, but if you come up on a recommended list or a history list like this, will you even be noticed? Not by me. I just blow past anything that I can't figure out. It's not worth my time clicking around reading something that seems random.
The fiction book above was released a month ago today and has 453 reviews already. He does little to no advertising and he gets promoted on Prime day and I get emails from Amazon about his books a couple times per year and he shows up in my recommended books list. I picked up the first book in the series as a freebie and I may have purchased one other. There are lots of things that make his books appealing to buy or for Amazon to promote. The big one related to thumbnails is the title (and generally clear graphics). The author name could be clearer for recognition and the image could be simpler, but the main thing is that title. Look at MJ's. Pretty clear title even with the dark red. You may have to work a bit to read the subhead if you you are drawn to the book, but there's likely enough there to be interested. They look professional and made to be viewed relatively easily.
That image was what was presented on my full size monitor. Millions of people also browse and buy on their black and white kindles. What do these covers look like there? Millions of people buy through their phones or devices by looking first at the cover not the description. This is how people do a quick evaluation through the possible choices when browsing through books. It's with a thumb flick on a device. If you can't get attention there, then nobody will look at your description. It's almost impossible to read the text of your title or the tag under it or tell that it's a skateboarding book from the graphic. Larger, clearer titles would help. If you were doing color, then good separation of colors are necessary. They should also not cause issues for color blind people. Google this "what combinations are bad for colorblind people" to be sure you don't violate that in your covers or packaging if you ever release something in color. In all three cases, the computer, the phone and my black and white kindle, I can't read the title of your book. That can be death to a book.
From the graphic, I also can't tell it has anything to do with skateboarding. It looks like someone ready to dive into a pool or a pond with some trees in the background or maybe someone holding a fishing rod or someone standing at attention holding a gun. There's also a dark line at an angle. Why would I click into it if I'm a skateboarder and I can't tell what it is?
You might look at a tutorial like this if you're going to be doing a homemade cover:
Creating the perfect cover for your Kindle Books
I understand that it was translated for you, but look at your description text critically as a buyer. Could you make that first question into a full sentence? Could you break the text into paragraphs to make it easier to read instead of a blob of text? Why is there a space before the question mark? Why do the other sentences have no space after the period? People may look at that and assume the text of the book is going to be difficult to read too. Does the text flow? The toilet sentence is kind of awkward. You seem to have a have a nice "look inside" setup. But will people bother to go look at it?
Amazon is intelligently run by computer algorithms and may show related authors or related books. Amazon is surely keeping track of how many people look at your book vs. how many buy it or how many people see the thumbnail vs how many click it. If they show your thumbnail and nobody clicks into it, will they keep showing it and at what frequency? If traffic comes to your description but doesn't convert because it doesn't look right or because your advertising was to too broad of an audience or you advertised a lot and it didn't convert, will they continue to promote you and again at what frequency? They have millions of books to promote. Why would they continue to show yours very often or at all if nobody clicks on your cover or buys from you when they do get a chance? You might still come up for suggested reading, but books with better stats will likely be promoted first.
Authors are likely heavily penalized in terms of amazon's promotion or search if someone runs a lot of ads say via google that drive traffic but don't convert for whatever reason. Amazon won't know the number of ads, but they can still tell conversion percentages. So optimizing cover and description is probably a good idea before promotion.
Good luck with your promotion.
