To “get back in the saddle” means to return to something after a break or absence, often after some kind of failure or setback. The phrase originated in the early 19th century, and referred to cowboys and other professional riders who had suffered an injury, but were now recovered and “back in the saddle” to continue their normal lives. By the late 19th century, it had begun to be used in the more general sense, to mean returning to any activity.
This episode is about Richard “getting back in the saddle” as he comes out of retirement.
The Annotated Gilmore Girls 