Hi firdous

It depends what caused the muscle loss. It is likely to be either a nerve injury that supplies the muscles in the arm or a direct injury to the muscle.

The only option available is strengthening exercises, although sometimes it is a good idea to combine this with a type of electrical stimulation (called functional electrical stimulation) - particularly if the muscle is very weak. The success of those exercises would depend on the cause and extent of the muscle loss.

I would not recommend you seek help for this online. You should have your problem properly assessed. I think you should consult a physiotherapist who can assess your problem and give you an appropriate programme of exercise.

Are you able to get physiotherapy?