Are you trying to set up a plan for a minimum term for example 3 months or 12 weekly payments but would like the payments to continue onwards after this until the customer chooses to cancel?
While creating a plan you will see the below 'Automatic Renewal' box. If you would like payments to continue after the minimum payment term you just need to tick this box, if you leave it unticked the payments will automatically stop after the minimum payment is made.