Rent Now is an optional service, so while many landlords find it a useful way to set up a tenancy (with the referencing, contract, deposit and rent collection all taken care of), there's no obligation to use it.
If you are unsure about how Rent Now works, you can see the steps involved in this useful guide.
If you don't want to use Rent Now, or want to re-market your property for now, you can simply cancel the application by clicking "Action" from your dashboard.
You can then choose Cancel / Reject Application Options to send the tenants a message, cancel their Rent Now application and refund the holding deposit.