In order to setup your secure withdrawal passcode to withdraw funds via app you may go to the withdrawal tab and initiate a withdrawal.
You will be prompted to setup the password as mentioned in the screenshot below.
You can choose your 5 digit code which will be used for your future withdrawals.
Once this step is completed you will see a confirmation screen as mentioned below:
Please remember to keep your code secure . In case you lost the code please don't hesitate to contact support via firstname.lastname@example.org for recovery.