If you're accessing your account on a mobile device, open the menu via the 3 lines in the top right corner of the screen:
The Account login link is in the bottom right corner of that menu:
From here you can enter your email address and password to sign into your account:
Once logged in you'll see your order history at the top of your Account page, scroll to the very bottom to find further account functions:
From there, click on Manage Subscriptions to go to the subscription portal:
From there you'll be able to manage your subscription with all the same tools as the desktop website (lots more how-to's on the other Help Centre articles here if you're unsure about anything!).