[b.rose]

is there a way to reverse these changes?

Usually, most changes reverse themselves after a certain period which can very considerabley from person to person.

Also what your experience/knowledge is about the root cause of this shrinkage, is it local (testicular issue) or brain/nervous system issue?
My life is very difficult now. Shrinkage is not the only problem. I have got joint pain, muslce pain, fat, low energy , dizzy and flu like condition all the time. Headache is another challenge. Every day is a challenge now.

It could be as simple as dehydration - try drinking an extra litre or two of water for a day or two. If that does not work then go straight to your doctor and get yourself checked out, particularly liver and kidney function.

You sound like you need professional medical advice rather then guesswork from the internet.