We had a whole discussion about that in January on the other forum:
Large Scale Central - Advanced Forum Detail Topic - How to properly test a live steamer on air
I don't think a hand pump will work, as you need your hands free to adjust, manipulate and otherwise deal with the loco. A garden sprayer, especially the type you pump up might suffice. I use a portable tire pump that I keep in my car - I do so few miles in retirement that I have to check my own tires, and air hoses at gas stations are becoming few and far between.
Anyway, the portable air pump came with a bunch of plastic nozzles for beach balls, boat fenders, etc. Usually one will be a close fit in a hole in your boiler - probably the hole where you fill it with water. [Not personally familiar with the Rocket.] Use tape to make it a better fit, but it doesn't have to be screwed in and it doesn't need to be tight. The air pump is producing air at 50+psi and your loco should run on 20-30psi.
So now you have a fit for the hose, I take the whole thing down to my SUV which has a 12V outlet in the back. I prop up the loco on blocks or rollers and start the pump. You should see the pressure gauge register something, and you can set the gear and open the throttle just as if it was in steam.
A couple of other matters. Do make sure you have oiled the motion (bearings, axles, etc.) And don't run it for long - a minute or two is fine but you don't have any emulsified steam oil lubricating the cylinders.