Dial #PWD# or #793# from your T-Mobile phone
Follow the prompts to reset your voicemail password or account PIN if that is the lock you mean
If you mean the SIM PIN, go to Settings
Open Security or Biometrics and security
Select SIM card lock or SIM PIN
Turn off SIM lock
Enter the current SIM PIN
If you forgot the SIM PIN, contact T-Mobile support
If you mean the phone screen lock, go to Settings
Open Lock screen or Security
Select Screen lock
Choose None or Swipe
Enter your current password, PIN, or pattern
If the device is managed by T-Mobile or an employer, contact the account admin
If you mean a network unlock, request a device unlock from T-Mobile
Make sure the device is paid off and eligible for unlocking