Does anyone know how my son would go about obtaining a paternity test?

My son and girlfriend gave up a baby for adoption a little over a year ago. He has had severe depression over the decision. He didn’t want to give him up, but the girlfriend pushed till he felt it was hopeless. He recently found out that his girlfriend had been unfaithful during the time she became pregnant. He would like to do a paternity test to determine whether or not he is the father. If he isn’t it would eliminate the pain he endures daily. Does anyone know if this is a possibility or how he would go about obtaining a paternity test? The birthmom has contact with the adoptive parents but my son doesn’t.