How do I reinstall sims 2 without a disc?

I got sims 2 free with a code on origin but i haven't played it in a while. Every time i try to open it now, it says i have to reinstall it. i watched videos and searched it up, but all that comes up is things that require a disc. One time, i found a result that isn't used with a disc, but i don't understand how to do it so now i need help. Hopefully one of you knows how to do this! (p.s.) I need to know how to use the game panel!