There are multipe ways to get to the withdrawal flow:

a.) Via the wallets screen

Step 1: Tap the wallets icon in the footer or the wallets row in the watch list.

Step 2: Tap the withdraw button underneath the list of your wallets.

b.) Via the wallet for an individual coin

Step 1:

Tap the wallet button in the quote detail section ...

... and then ...

... or the wallet amount on the wallets screen.

Step 2: Tap the withdraw button.