What kind of a family support i can give to 27 year old son with psychomotor retardation due to depression?

Many ways: Love. Helping him get to appointments if he is too impaired to do that on his own. Supporting his use of counseling and psychotropic medication use. Letting him know that he is accepted regardless of having a mental health illness. I am glad that you asked.

Exercise: It would be so helpful if you did it with him and several times a day. It can start with easy exercises like leg lifts when your sitting down of moving your ankles. Walking is great.