Set a passcode on iPod touch
For better security, set a passcode that needs to be entered to unlock iPod touch when you turn it on or wake it. Setting a passcode turns on data protection, which encrypts your iPod touch data with 256-bit AES encryption. (Some apps may opt out of using data protection.)
Set or change the passcode
Go to Settings > Passcode.
Tap Turn Passcode On or Change Passcode.
To view options for creating a password, tap Passcode Options. The most secure options are Custom Alphanumeric Code and Custom Numeric Code.
Change when iPod touch automatically locks
Go to Settings > Display & Brightness > Auto-Lock, then set a length of time.
Erase data after 10 failed passcodes
Turn off the passcode
Go to Settings > Passcode, then tap Turn Passcode Off.
Reset the passcode
If you enter the wrong passcode six times in a row, you’ll be locked out of your device, and you’ll receive a message that says iPod touch is disabled. If you can’t remember your passcode, you can erase your iPod touch with a computer or with recovery mode, then set a new passcode. (If you made an iCloud or computer backup before you forgot your passcode, you can restore your data and settings from the backup.)
See the Apple Support article If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled.