Comments on the vendor video:
Personally, I've found that running a 30Hz tone brings out alignment issues (allowing them to be noticed and corrected) better than finger pushing, but I would expect the latter to be quicker and require less equipment (zero). If there are no alignment issues, either is probably sufficient.
I always cut out the foam surround where the screws pass through the frame (after gluing the foam, and prior to reinstalling the gasket). Last thing you want is to torque down the mounting screw to have the foam rotate and distort. If you're using clamps (vs screws through the frame), this isn't an issue.
Cleaning (and gluing to) the backside of a cone is a bit trickier than what was shown for the C-V front-side example in the video, but take your time. Presumably the written instructions with the kit will describe the process for your drivers.