Change your Apple ID - https://support.apple.com/HT202667 - "Follow these steps to change the email address that you use as your Apple ID." Plus special instructions if your Apple ID ends with @icloud.com, @me.com, or @mac.com. You may also wish to turn off "Find My" before changing information and turn it on again afterward.
What to do after [or before] you change your Apple ID [email address] or password - "After you change your Apple ID email address or password, you might need to update your sign-in information with any Apple services you're using." - Or if you're seeing persistent disabled messages or repeated requests for the password to your previous Apple ID.
https://support.apple.com/HT204071
Set up Find My iPhone on all of your devices - https://support.apple.com/HT205362
Home screen > Settings > [your Apple ID] > iCloud > Find My > turn on/off