How to delete an Apple ID
How do I delete one of the apple ids
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For information about how to delete an Apple Account (formerly “Apple ID”), read this support article —> How to delete your Apple Account - Apple Support
Carefully and thoroughly read that article for information about what happens when you delete your Apple Account. For example:
"Make sure that you sign out of all your devices to avoid issues with apps that use your Apple Account or iCloud. After your account is deleted, you can’t sign out of iCloud or turn off Find My iPhone Activation Lock on your devices. If you forget to sign out, you might not be able to use your device when your account is deleted."
If you are not absolutely certain you want to never use the account again, an alternative is How to deactivate your Apple Account - Apple Support You can do that and then delete the account later once you are certain.