How do I disable Find My and change password on iPhone XS Max?

Changing the password will not disable Find My.

Is that really what you are trying to do.......disable Find My? That's not difficult.

Tap Settings > Your Name > Find My and change the slider from On to Off

Or, are you really saying that you have forgotten your Apple ID Password, so you cannot get into the settings on your phone to make changes?

Are you saying you don't remember your Apple Account / iCloud password?

If so, click here ➜ If you forgot your Apple Account password - Apple Support