This is a difficult question to answer because there are many factors that can affect an author's earnings, including the price of their book, the number of books sold, and the royalties paid by Amazon. However, based on Amazon's 2018 report, the median revenue for self-published authors was $5,000. This means that half of all self-published authors earned less than $5,000, and half earned more.
There are a few things you can do to increase your earnings as a self-published author on Amazon. First, make sure you are pricing your book at a competitive rate. If your book is too expensive, potential customers will be less likely to buy it. Second, try to promote your book through social media and other online channels. If you can generate interest in your book, you're more likely to sell more copies. Finally, consider enrolling your book in Amazon's Kindle Direct Publishing (KDP) program. This program allows you to earn royalties of up to 70% on each book sold, which is significantly higher than the standard rate of 35%.
Enrolling your book in the KDP program is one of the best ways to increase your earnings as a self-published author on Amazon. If you're not currently enrolled, I recommend you look into it. You can find more information about the KDP program here: https://kdp.amazon.com/.