When you spin the prop and keep open throttle there will pass fuel into the cylinder.
If in doubt, put the plane inverted on a plane stand and start the engine with the carb pointing up

You can also remove the glow plug and pour (very little) fuel directly in the cylinder.
Just be careful, there's something called hydrolock. This is when you have to much fuel in the cylinde and the piston can't move freely.
If you then force the piston you can break the engine.
It should be tight, but if it's almost impossible you have to much fuel in the cylinder end need to empty it. Remove glow plug and spin prop to vent out the extra fuel.