To cancel a recurring buy, go to the Crypto section in your Wealth tab, and tap on 'Recurring buys'. Select the the recurring buy you want to cancel and you'll see the order details. You can either 'Deactivate' or 'Delete' it.
If you select 'Deactivate', the recurring buy will still be visible in your list, but will no longer go through. You can reactivate it at any time.
If you select 'Delete', the recurring buy will be completely removed. You won't have the option to reactivate and you'll have to set up a new recurring buy if you change your mind.