How would I treat a Seroma that has turned into scar tissue on my abdomen? (photo)

Thanks for your picture. If there is no more fluid, I agree that massage and time (3-6 months) could improve this area.  The only other remedy would be surgical removal.Good luck.
Earl Stephenson, Jr, M.D., DDS, FACS

A seroma should be drained periodically until no further fluid accumulates. Failure to do this will and with reorganization and formation of a hard mass it may take years to totally dissipate.

Since I do not see a scar around your umbilicus I assume you had either liposuction or perhaps a mini-tummy tuck(?).  This can go away with time as it settles down.

Very difficult issue to treat. I recommend ThermiTight RF or ThermiSmooth RF therapies under local anesthesia or topical anesthesia... 

I am not sure what type procedure you had performed. I presume it was either a tummy tuck or liposuction. Seromas can occur after either of these procedures. Initial treatment is usually aspiration and compression over the area with an abdominal binder or ace wrap. If you are six weeks postop