Is there a surgery to recover balance after tbi and it has been at least 3 years since the injury?

Depends on injury. The nature. Location, and severity of the tbi may give some clues as to the area of injury. For example, a common site of injury is to the skull base in the region of the temporal bone. This may lead to vestibular problems and subsequent balance issues. A neuro-otologist can help with this. Post-traumatic hydrocephalus/normal pressure hydrocephalus can lead to balance issues. Consult neurosurgery.
Possibly. You should discuss these findings with your doctor. You could reopen the cervix to drain the fluid, but, given the paucity of symptoms, that may not be necessary.