Manirahul,
I assume when you say the symptoms have returned, that it is the numbness and tingling in the fingers, with pain there also. That he is getting the numbness when grasping and during the night. Also, since it has returned, I am assuming that he did have a period of time where the symptoms were gone.
It is unfortunate that this has happened. He has tried using his splints again at bedtime, I hope, to help with these symptoms (if he is having night problems).
When symptoms return after a surgical release, it can be quite a problem. Usually, when a patient has had resolution, then a return of symptoms, it means that the patient is developing scar tissue around the nerve.
As opposed to the patient who never gets any relief from a release, here, there has probably been an incomplete release of the transverse carpal ligament. In these cases, a second surgery to make sure a complete release is done, usually has a good success rate.
But, when there is the development of scar tissue, the results of a second surgery are not very good. The nerve not only has to be released again, but then usually protected with something in the hopes that scar tissue does not form once again. So, this is quite a bit larger of a surgery than just a simple release.
So, you can try the medication for nerve pain, such as gabapentin (Neurontin) or pregabalin (Lyrica). Also, occasionally, a steroid injection into the carpal tunnel will soften or break up the scar tissue. But, if these measures do not work, and the symptoms are unbearable, then surgery may be necessary.
Good luck.