Large Scab Covering Nipple Still After 3 Weeks of Breast Reduction, How Can I Help It Fall Faster?

At this stage you need to allow your body to heal.  All you can do is maximize your body's healing potential by ensuring you eat a healthy diet (protein, vitamins etc) and that you don't do anything that will slow healing (smoking, excesive physical activity that disturbs the healing wound)

Follow your plastic surgeon's wound care treatment.  It may take while but it will eventually heal.

Although frustrating, the types of wound healing problems/eschars that you describe require time and patience on your part. In my practice, I leave the eschar or scab alone as I believe it behaves as a "biological Band-Aids”  for the underlying tissues.

 Continue to follow up with your plastic surgeon who is in the best position to advise you accurately.

 Best wishes; hopefully, you will be very pleased with the long-term outcome of the procedures performed.

Be patient. The eschar has to separate, and I would follow your surgeon's advise with whatever wound care he/she recommends. Good luck.