How do you access a hacked icloud where the hacker changes the ID and password?

See the following from If you think your Apple ID has been compromised - Apple Support

If you completed the steps above and think your account might still be compromised, contact Apple Support.

Then you likely will be unable to regain access. Be sure that you use strong passwords, that you do not share those with anyone, that you do not reuse passwords across accounts, and that you enable two-factor authentication on your account. You weren't hacked per se, you more than likely fell victim to poor password/account management.