Physician asst new patient

two questions

First- if we bill a follow-up with a PA where the physician did the initial visit, incident to,what qualifying code go I use in block 17 with the physician NPI?

Second- if a Medicare NEW patient is seen by a physician assistant, what do I put in block 17 and what qualifying code do I use? Do I use the supervising dr or the physician that referred the patient to our specialist ?

Physician asst new patient