How do you do it what do you need to do. It doesn’t tell you how to get the gear to stay on?
We need some more information regarding what specifically you are trying to do to give you detailed help.
There are a variety of ways where you can have a gear stay in position on an axle. Set screws, clip rings, shaft collars, etc.
I have looked at it again and the axel has a notch for a along it. the gear has a like notch the same size and I cannot figure out what came to make it lock. because so far I think I need a pin that locks the axel and gear so they spin at the same time.
Edit: I have recently thet what I am looking for is a key and that it isn’t in the kit… we have sent out a pair to get one hopefully for us.
When you’re dealing with gears, sprockets, etc. in high torque applications you need to secure the gear from slipping on the shaft with a key. If you are talking about the BaneBots CIM gearboxes, the output shaft has a 1/8" key, so you will need a gear with a 1/8" keyway. If you can’t find one, you will have to get one without a keyway and cut one yourself.
Key can be found at McMaster, just search for 1/8" key stock.