I may have been hacked

Unfortunately, you seem to have contacted one of the thousands of scam “tech support” sites. If you allowed them to access your computer, immediately change all passwords that have ever been used on that computer. If you provided financial information, immediately contact your bank.

You change all passwords by individually changing them, one by one. You should know better than us what accounts and passwords you have, and thus what passwords you need to change, aside from obvious ones like the Apple ID password.

That would depend on which password you need to change. Consult the appropriate web site for each service where you wish to change passwords.