Click on the Appointment and Edit Invoice.
Add an item number and enter in any other additional details or indicators, plus repeat for additional items, as necessary.
Save when done.
At the end of the day (or whenever you wish to transmit claims), go to the Bulk Bill area:
By default Medilink will have a Send All button shown - typically you would simply use this. You can review and check off specific ones in Invoices Due though (which I have done here) then click Send Seleted.
After transmitting claims you should also review your previously sent claims via the Pending Claims tab. Here you can view Processing and Payment Reports and Settle them (i.e. apply the receipts and adjustments to the claims). Use the Settle All button to do this quickly.