Open Settings
Tap Screen Time
Tap Change Screen Time Passcode
Tap Change Screen Time Passcode again
Enter your current Screen Time passcode
Enter a new Screen Time passcode
Re-enter the new passcode to confirm
If you forgot the Screen Time passcode, tap Forgot Passcode?
Enter the Apple ID and password used to set up Screen Time
Follow the prompts to create a new passcode
If you cannot reset it with Apple ID, erase and restore the device from a backup
If needed, contact Apple Support