Check your original T-Mobile account welcome email or paperwork for the account PIN
Log in to your T-Mobile account and look under account security or profile settings
Use the T-Mobile app and check your account or security settings
Call T-Mobile customer care and verify your identity to request or reset the PIN
Visit a T-Mobile store with a valid ID and ask a representative to help you recover or reset it
If you set a custom account PIN, try any PINs you may have chosen during account setup
If you forgot it, ask T-Mobile to reset the PIN after account verification