A forgotten guest key can be reset by any adult as long as that person knows the password that they use to sign in to their Microsoft account on the console. The adult must be signed in on the console to reset the guest key.
Use your password to reset your guest key
Press the Xbox button to open the guide.
Select Sign in.
Scroll down and select your account to sign in.
After you're signed in, press the Xbox button to open the guide.
Select All Settings.
Select Signed-out content restrictions.
Enter your Microsoft account password to confirm your identity.
Note If you forgot your password, select I forgot my password, and then follow the instructions.
If you can't reset your password using the security code that was sent to your alternate email address or phone number, you may be able to recover it online. For more information, see Recover your Microsoft account.
Select Remove guest key.
If you have forgotten the guest key, enter an incorrect guest key three times, and then enter your Microsoft account password to remove the guest key.