This screen appears when the TenX Wallet app is sent to the background and stays there for a certain period of time, or on first open.
This passcode is not permanently stored; a new one is set on every login.
If your device has fingerprint login set up, you can use this instead of manual PIN entry.
If your device is set up for Apple FaceID recognition, you can also use FaceID to unlock the app.
If you are unable to remember your 4 digit lockscreen passcode, you can clear app data or reinstall the app. This will log you out of the TenX Wallet app as well as clear all cookies involved.
You may then log into the TenX Wallet app again, and be allowed to set up a new 4 digit passcode.