If you want to set a master password, go to Settings. Choose ‘Master Password’. Type a master password.
Make sure that you don’t forget your master password. Your master password will be stored only on your device. Therefore nobody will be able to access it, not even the ColorNote team. To prevent others from accessing your locked notes, including the case where the device is lost, ColorNote doesn’t provide an option to find the master password. ColorNote places heavy emphasis on security.