Put the blade on your balancer so it is horizontal. The side that falls it too heavy. You can either sand the heavy side or put some clear nail polish or something like that on the light side. Don't change the props airfoil. The horizontal balance tells you which blade is heavier.

Now put the blade on your balancer so it is vertical. One side will fall. The vertical balance tells you which side is heavy laterally, just like when you do a lateral balance on your airplane.

You know the blade is perfectly balanced when it will stay in whatever position you put it in on the balancer. If it moves when you let go of it, it is not balanced.

My advice to you is to forget about it on a trainer because it's not worth it...