How do I flip the viewfinder image on an old (~1985) Panasonic video camera, Model #PK-980?

I have an old Panasonic video camera from the mid 80’s. This is the kind that has a separate VCR and a camera head that looks like a full size TV camera. (Newvicon Omnipro) It was the top of the line at the time. The viewfinder is a separate unit that can be used on either side of the camera by flipping the housing. However the image is upside down. There has to be a way to flip the image but I don’t see it.
The viewfinder model number is PK-M059. The camera is a PK-980 but it is the same as a PK-959. Any ideas? I have been all over this thing. There has to be a trick I’m missing.