I have attached a guide on how to send recalls. Hope that answers your question.
To specifically look for high priority patients, in the recall screen, there is a drop-down for which priority patient you interested in on the left side of the recall screen. By default, every patient is set to Normal Priority. To set a patient up as high.
Go to the patient record.
Click Comms Tab
Select the button "details..." next to recall information
On the patient recall details screen at the very bottom, you can change recall priority from normal to high.
Click Apply and OK to save.