When first logging in to your CoinCorner account on the app, you will be asked to provide your email address, password, Google Authenticator code (if 2FA is enabled) and to choose a new 4-digit pin.
This 4-digit pin will be saved as long as you remain logged in to the app and as long as the app remains installed on the device. Upon closing the app (but remaining logged in), when you go back to the application you will be prompted to enter the 4-digit pin before you are allowed back in to your account.
This 4-digit pin will remain the same as long as you remain logged in and keep the app on your phone. However, if you log out you will be asked upon re-opening the app to choose a new 4-digit pin for your account.
If you forget your code then you can reset your 4-digit pin simply by deleting the app from your device and re-downloading it from your respective App Store. When you open the app after re-downloading you will be met with the same login page as seen above, where you can choose a new 4-digit pin for your account.