As you can see in the screenshot below, there is a new column called Patient ID. If the column is not empty for the highlighted Customer, the button gives you the option to Detach Rx Patient (as shown). If the Customer does not have a Patient ID in the column, the button changes to Attach Rx Patient.
Clicking the Detach button removes the Patient ID (use this if the wrong patient gets attached). Clicking the Attach button pops up a search screen with the patient records from the pharmacy system. Select the applicable record and it is now attached to the Customer.
In some cases (pharmacy system dependent), demographic changes in the pharmacy system will update the Customer record in the POS. In no case will changes in the POS sync to the pharmacy system.