Re: EA app says that sims isn't downloaded on my computer when it is

@Maryem1602  Please clear the EA App's cache and restart your computer.

https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/

If that doesn't help, you can try downloading Sims 4 again.  This will only affect the game's program files, and it might be a quick process if the EA App simply verifies the data's presence and finalizes the install.  (This happens often but not always.)  If you want to back up your saves and otehr user data anyway, which is a good idea in general and regardless of any issues you're seeing, those files are all in Documents > Electronic Arts > The Sims 4.  You can copy this entire folder to a separate location, ideally on an external drive or USB stick, but elsewhere on your computer works as a temporary backup too.