To change the type of password used in the DFNDR's Vault, open the app, tap on Tools tab and select the Vault feature.
Enter your pattern.
Tap on "Settings" (engine icon).
Select "Change your password".
Select "USE A NUMERICAL PASSWORD" at the bottom of the screen.
Create a 4-digit numeric password.
Reenter the password to confirm.
Now, just select "FINISH" and it's ready!