1996 MGM transmition reverse problem...

[Hombrero]

driving 1995 MGM, with 56000 miles, great car, no problems at all, last Friday, I shifted into reverse and engine started accelerate but car didn’t move at all, I shifted into D, car moved, I tried reverse again, no move at all, I turned engine off, tried again, same problem, I started driving home and I tried reverse at home, it was working, transition oil is nice red clear, no strange odor or smoke, any ideas what’s happened? My friend told me that solenoid could be problem, can I change that at home by myself? THX