Here is how to set up Face ID or Touch ID again.
Open the Settings app, tap "Apps" at the bottom to show the app list, and select My Calendar. Then turn on Face ID or Touch ID.
If the option is not there, open this app, temporarily turn off "Passcode" in the settings screen, then turn it back on and set up your passcode again.
If that still doesn't work, please contact us via the "Contact Us" button at the top right.
Thank you.