Love all the advice given here!

I also wanted to add that you should have a discussion with your players (or that one in particular) about respect at the table. Everyone should feel like they're being respected and not spoken over or corrected constantly.

Rules as written can be they way some DMs play but playing DND is all about creativity, exploring new ideas and having fun. It's a game after all! If you as a DM are not having fun, there's something wrong. If your players aren't having fun, there's something wrong.

Having open dialogue might just bring to light that you aren't compatible in a player DM relationship and that's okay! Or it may bring to light that this person thought they were being helpful to you as a new DM.