dear friends tell me how to make a keyword steable?

This is because your competitors are ranking higher. You need to work on continuous off page techniques to keep your ranking stable in search engine pages.

It is because your site and competitors website is competing in the same keywords so there will be fluctuations in search.

Keyword rankings often fluctuate, which is common in SEO. However,  there are a few things you may have to focus such as; keywords competition, competitor rankings and long-tail keyword selections.