Man rejuvenated and taken to alternate universe planet earth during cave man era. The aliens he'd rebels who were trying to undermine project. He was placed in small area of upper portion of cave he was supposed to be in. He contacted ship leader and was transferred to correct location. Later ship left area, but as he made contact with natives, changes were continuing to be made so he identified the AI left behind. Thought I had it but can't find through searching.
