To make a withdrawal:
Tap on the Account tab, where you will again see a button saying either ISA, GIA.
Switch to the relevant account - if you just have a GIA, you will only see this!
Scroll down and tap on the Withdraw button.
Type in the amount you would like to withdraw and press Confirm withdrawal.
Withdrawals typically take 2-3 working days to reach your linked bank account but can take up to 5.