Go into the actual tax form by clicking forms in the upper right-hand corner of the screen. Then go to form 1099R Summary, Line 44 and enter in the correct RMD amount. This amount should now appear when you go back into Turbo Tax and are shown what your entered RMD amount is. I spent a lot of time trying to make the change through Turbo tax between my IRA and an inherited IRA. I hadn't withdrawn enough to cover double the amount of the RMD and so the program was ready to create new forms for the penalty I would have had to pay! What a pain.
