Seem to remember seeing a video of a Honda gearbox oil change where the filler was a black plasic/rubber plug with a curly 'handle' on top. Under the air filter.
The 'mechanic' spent a long time dealing with removing the air cleaner and associated air pipes to access and expose this plug!
Filling seemed to require removing a level plug on gear box, parking on a flat surface (with wheels back on ground??), then filling sloooowly until oil dribbles out of level plug hole (or, I guess, you've poured in a volume equal to what was drained out)
All sound a bit of a phaff