Ask support to close the account. Open Help in DoesQA and select Create new ticket.
Include the account email you want closed, and that you want the account deleted or closed.
If you only need to stop billing, cancel the subscription first. See How do I cancel my subscription?. Only the Account Owner can cancel.
If you are leaving because something in DoesQA is unclear or a run is failing, say that on the ticket. Support can often help before you close the account.