My ten year old MacBook Pro has been returned to me by a family member after a longtime loan!. It is running macOS Catalina Vers 10.15..7. and is very very slow. I have reinstalled the OS but it is still running very very slowly. I would like to return the computer to factory settings but can find no way of doing that. Advise please on whether this is the best course of action and how do I do it in Catalina?