If you are an Account owner or a Controller, go to Expense claims > History. Click on the transfer and then cancel. The related expense claims are sent back to Expense claims > Schedule reimbursements where you can reset an execution date for instance.
You can cancel your transfer as long as we (Spendesk) haven't started executing the transfer: it means that as long as the status is either "waiting for confirmation" or "pending", you can cancel it. Otherwise, once the status is "processing" or "paid", it's too late, we can't cancel it anymore.