Hello,
You must use Honda hydrostatic fluid in the transmission. If the level got that low, you may have to bleed the air from the system. There are instructions online from Honda on how to do it. I believe the transmission must be removed and sort of oscillated in a circular motion.
My Honda HR215 mower has the hydrostatic transmission, but the cap has a built in dipstick, not sure on the model from overseas.
Regards
Jeff