I need to know what to do with my own website, because its rankings have fallen, and I want to try to fix the situation now. Is it possible to do this on my own, without the help of SEO specialists, do you think?

Why not? Anything is possible nowadays, because there are many useful websites and tools on the Internet that can provide you with a lot of information and useful tips. For example, I am currently tracking the effectiveness of my website using this resource, constantly checker the ranking of keywords https://pr-cy.io/tools/keywords-rank-checker/