If you forget your password, or have some other concern, you can reset your account by logging out, entering your email address (the one the account is registered to) in the login screen, and tapping "Reset account". Tap "Sign in", enter your email address, and tap "Next". You will then receive an email from CryptTalk customer support with a new activation code. Enter the code into the field provided, tap Next, and set up a passcode. After this, you will be ready to use the app again.
Please note that this will delete all of your personal data stored on the device such as call history, but not your contacts.