Just installed the AGNSS kit. Very well designed!
Because it was so recently released, there was not a dedicated video in English so I was basing my install off the Reach videos.
So here are my thoughts and tips (some are general practices):

lift the gimbal housing up slowly to reveal which way the ribbon cable can bend.
When unplugging the two cable at the front (Compass where the wires go into the legs) be aware that you need to press the sides in on the molex plus and there may be glue (same colour as plug) holding it in... my wires pulled out of the plug.
Like in the video...don't put the 3 screws holding the new gps board on back in. Just use the external nut, you need the 1mm the screw head takes up.
Since the agnss board has a 3d printed clip, be careful not to bend out of shape the foil that it is going to clip onto. The foils has one screw and holds a patch antenna. Otherwise your clip may not conform to the foil.
When putting the base/legs back over the main electronic body watch to see if the forward and rear cameras are 'rolling' the foam ring seal down in front of the lenses. (I simply removed the foam seals)
Before screwing down the base (two halves) power up the P4 and RC to ensure you have a Link. NB: be careful with the gimbal when powering up. If no link, try again without the gimbal ribbon attached. ( I had to use the original ribbon).
Careful not to squash any cables between the two halves.
Do not over tighten screws that go into plastic
The solder used in these things can seem to take a lot of heat to melt. To help, 'add' your solder to the iron. Suck it off later. It increases the surface area of heat you are applying and dilutes their solder to a lower melt point.
Colour code screws and the holes can prevent you putting long ones in shallow holes etc.