To add additional form(s) to an existing appointment follow the steps below:
Select the appointment preview for the appointment you want to add a form to > Select the Edit appointment button
Select the Forms tab on the left hand side > Select Add forms to appoitnment
You'll be taken to an Add new form area > Search for the form name in the search area then tick the box next to the form > Select the Save button at the bottom to add
The form will now be added to this appointment
