The recurring GoCardless bank account payment will be linked/aligned with the same schedule of the assigned membership.
Head to your 'Clients' tab, then select client
Go to 'Services' tab
Click '+ Assign Membership' and choose the appropriate membership to assign
Enter the 'Membership start date', along with any other changes to the membership on the form, then toggle to turn on the 'Setup linked Gocardless payment schedule' checkbox.