I would like advice on how to win a tribunal appeal

Hi everyone.
I am looking for some advice if anyone can help me please?
My husband failed his work assessment with the dwp, and also the mandatory decision. 
There was quite a few in the results that were untrue, we asked for him to be seen at home as
He was involved in a serious car accident in Feb 2018, which has left him with physical injuries, and very bad PTSD.
The assessment officer was a physiotherapist, although I feel not qualified to deal with mental health conditions, which cannot be addressed for another seven months on the waiting list.
He rarely goes out of the house, sits in the back of the car blind folded, as he is so frightened.
Further conditions that relate to PTSD.
I would like advise to how to possible win the appeal in a tribunal. Does he have to go or can I  represent him.
I am very disappointed with the dwp to have to put us through this ordeal especially as the car crash was not his fault, and he is unable to return to his job......He is presently on universal credit as a joint claim.
Hope you can help
Kind regards