How can I unlink my Threema ID from an email address or phone number?
If you want to remove an account link of your Threema ID (e.g. with your phone number or email address), simply go to the “My ID” page (Android: info icon next to your ID in the main menu, Windows Phone: Navigate to “Me), tap on the number or email and remove it.
If you no longer have access to the respective ID, you can remove the account link online. To finish this process, you must have access to the linked email or phone number.