SEO snippets not showing on Google

With my first site, Yoast showed my customized snippets on Google, but it didn't work for my friend who used to control our second site, and I control it now, so I wanted to try Yoast on it myself, but Yoast is no longer on the installed plugin list, and when I try to reinstall it, it says that there is already a file at the destination, which I am struggling to find, so I tried AIOSEO, which didn't give me my desired result, so do y'all have a guaranteed alternative?

It doesn't have to be a fancy SEO plugin that does everything; I just want to show my own snippets on Google.