There is really no way to open Locked Notes on your iPhone, in case you forget the Password for the Notes App. However, you can Reset the Password for the Notes App on your iPhone and start using this feature once again.
Reset Notes App Password On iPhone
iPhone allows you to Lock Notes with a Password, providing you with a second layer of protection for your personal data, hidden photos and any other data that you may want to keep protected on your iPhone.
However, the Password for the Notes App is not the same as your Lock screen password and this increases the chances of forgetting the Password for the Notes App, especially if you are not using the Notes App on a regular basis.
As already mentioned above, there is really no way to open Locked Notes on your iPhone, in case you happen to forget the password for the Notes App. The only option in such a case is to Reset Password for the Notes App and start using this feature to protect New Notes.
Unfortunately, Resetting the Notes App Password does not unlock any of the previously Protected Notes on your iPhone. The Notes which you had protected previously will continue to retain the old Password and cannot be unlocked using the New Password.
Steps to Reset Notes App Password On iPhone
Follow the steps below to Reset the Password for Notes App on your iPhone.
1. From the Home screen of your iPhone, tap on the Settings App.
2. On the Settings screen, tap on Notes.
3. On the Notes screen, tap on Password.
4. On the Next screen, scroll down and tap on the Reset Password option (See image below).
5. You will be prompted to Enter your Apple ID and Password.
6. On the next screen, type the New Password for the Notes App, verify the Password and also type a Password Hint (optional but recommended).
Once you Reset the Password for the Notes App on your iPhone, all New Notes that you create using the Notes App will be protected with the New Password, while older Notes will continue to retain the old Password.
Note: The Notes App Password Reset will be reflected across all your Apple Devices, in case you are using iCloud Notes or iCloud Keychain.