You haven't said what your flying experience and skills are, but given the topic I'm guessing you haven't been at this for a long time? To fix your plane, you really need to go through a basic trimming routine. The first task is to get the CG set properly and the control throws at a happy place. For a trainer, I don't bother with the inverted upline that most aerobatic pilots do. I just cut the throttle and watch the plane glide. If the nose drops quickly and I can't hold it up with the elevator without applying the throttle, the plane is too nose heavy to be a good trainer. A similar test is to simply get a feel for how the plane lands. If I can't hold flare with the elevator until the plane is moving pretty slowly, it's too nose heavy. So I move the CG back until it drops smoothly and I am able to flare the plane properly for landing. Too rearward a CG results in a plane that glides shallow and drops out of the sky very suddenly. That CG tuning method will get you in the happy zone to make a good flying trainer.

The second task is to check for thrustline. Trim the plane at WOT for straight and level flight, then chop the throttle. Observe what the nose does. If it IMMEDIATELY drops, you need more downthrust. If it IMMEDIATELY rises, you need less downthrust. Note the bolded "immediately" in both descriptions. A plane the smoothly lowers its nose as it loses airspeed does not have a thrustline problem. Thrustline problems are when the plane changes pitch or yaw due to thrust. It's hard to see that happening when you punch the throttle, so the best test is to look for it when you cut the throttle.