Guys I have a laptop I want to replace it thermal paste myself becuase it's having heating issues

I have a dell precision 7510 laptop, got scammed first time a guy literally didn't bother to even remove the old thermal and put a very cheap one above it directly closed the laptop and said everything is done paid him same day laptop was shutting down, then took to another repair shop he opened it in front of my eyes that's why I saw the bad thermal paste, he replaced it, I paid him,took my laptop was working fine for 2 weeks, but in week 3 it started to heat again.

So I hate this but I think I have to do the replacement my self becuase I paid alot of money but I am just scared to screw up my device especially since it's the only laptop I have only desktop device I have, also this will be the first laptop I try to fix my self, I don't have any experience in doing this, any help about what should I do, idk what happened to people these days scammed from two different people this is just too bad.

What should I do? you all, I need help, really ?