Sometimes a client wants an extra design option that isn't in your standard collection. You can add individual templates to their booking without changing your collections for everyone else.
Manage → Bookings → Select a booking
Click the Designs tab.
Click Start New Design.
Choose whether to use a template from an existing design collection or upload custom artwork for this specific booking.
This only adds the template to this one booking. To make it available for all future bookings, add it to your design collections instead.