Hold full down on the elevator stick. That will force the rear down and hold the nose up. Hold that for a few seconds as the plane accellerates then slowly let up on it. Don't hold it to long because it may force the plane up in the air before it's ready to fly.. then you have a whole different set of problems.

This is normal for tail draggers.. just hold that stick to full up (meaning pull it all the way back before you add throttle, then hold it there as it starts to roll for a few seconds then let it go then take off normally.

You just need to get some air passing over the wing and horizontal stab and get some effectiveness in the control surfaces to let them do their jobs.

CGr.