When you change a diaper on an airplane you should take your child to the bathroom in the airplane and change the diaper there.
In the airplane bathroom there should be a trash can or waste bin that could be near the toilet with a lid on it.
You can then just put the dirty diaper into the trash can after you change your babies dirty diaper.
Do not leave the dirty diaper just laying on the toilet or on the floor.
Always put the dirty diapers into the trash can and then wash your hands and the babies hands after you change their diaper.