New to this, not entirely sure how it works,

Hello my name is Rachel, I have a son who is 17 and trying to get some advice for him as there doesn't seem to be much help anywhere else . Anyone had an assessment for Low Capability for work as an appointee? My son is 17, likely leaving education this summer and he has communication difficulties similar to Selective Mutism and he is also Autistic with daily and mobility needs, I am trying to see how I would be able to get Low Capability for work related activity as he would really struggle, doing interviews, courses etc. the college he is at is a special needs college and he is struggling there. I had to become an appointee as he struggles even passing security on the phone to discuss his Pip etc and wouldn't have a clue about filling forms in etc as his mental age is much lower than his chronological age. Any help is much appreciated,