2010 Toyota Prius - Integral Rear Passenger Seat Belt Replacement

Hi Forum-
My dog is in a bit of trouble today having chewed through my mothers seat belt while she kindly watched our Brittany over the weekend. Dog is fine but the passenger rear seat belt on my Mom's 4-door 2010 Prius is nearly chewed through (this is the seat belt for the center/middle passenger). I found a new Toyota replacement part online (73350-47030-E0) for $108.28 @ Toyota Online Parts.

What I don't have are the instructions to access the inside of the rear passenger seat. This is the 60% rear folding seat where the seat belt tensioner is inside the seat itself.

I was able to remove the rear seat trim, cover, and padding on the backside of the 60% fold down seat. This was quick and easy. It revealed no immediate access to the seat belt assembly (just what appears to be the outside mount base that the tensioner affixes to from the inside of the seat?)

Anyway she/we almost never use this seat but it needs to be replaced. I'm handy with car repairs, entirely on classics, and have tools but this is more modern than what I typically work on. That said I'm not about to pay the dealership $400+ to do this. It can't be hard.

Does anyone have experience with this seat belt replacement? Does the front of the seat's upholstery and padding need to be removed to access the interior of the seat frame (where the tensioner is affixed)? Any links to the instructions, PDF, or photos of the assembly manual would be deeply appreciated.
Thank you,
Matt-
Raleigh, NC

 

Chap I appreciate the lead on the repair manual. I'll look into that. Figured this wasn't a common repair so we'll see if I can be the first to detail the process.