Fly straight and level, bring throttle to idle, as the plane slows feed in up elevator to maintain altitutde. As you slow down the plane's nose will point further and further up. At some point the plane will stall and the nose will drop. At that instant apply full rudder. That should be enough to induce a spin. If it doesn't spin, then help it along by applying full ailerons in the same direction.

There are variations on the theme.... but that should do it to begin with.

If your plane's CG is too far forward the plane will not stall it will just slow down and mush along, perhaps entering a gentle dive.

If the CG is too far back you may find the plane won't come out of the spin on its own. If your model is conservatively balanced that is not likely to occur. Search a bit and you'll find plenty of info on how to recover... if recovery is possible.