Is there a surgery that can help with mental retardation?

Hmmmm: "mental retardation" is too broad a term to be able to give a helpful answer. In rare cases, maybe. Typically, no..

No: Mr is a functional diagnosis. I am not aware of any structureal abnormality or connection abnormality tha tcan be improved with surgery.

No specific surgery: Brain surgeries may be done to treat uncontrollable seizures, remove brain tumors, shunt excess cerebrospinal fluid build-up that puts pressure on the brain, open skull sutures that closed prematurely, repair blood vessel malformations or reduce the impact of brain trauma. They often improve a child's health and chance of survival; some help preserve cognition or allow development to proceed.