In the Notes app How to lock or unlock notes on your iPhone or iPad.
If you’re using a custom password, you can switch to using your device passcode. When you change your locking method, notes that you accessed with the previous method begin using the new method.
Go to Settings (at the top-right corner), then tap Remove.
Opening one locked note opens all your locked notes in the same account for several minutes so you can easily jump into another note or copy and paste information from other apps.
Go to the Notes app Set a passcode on iPad