You may grab the spinner with the prop turned "off compression" and have someone else hold the tail up with one finger underneath. The heavy side will drop. As the previous poster said lay pennies or washers on the "up" wing until the plane levels.

Just a note: If the plane was uncontrollable, I would be more concerned with checking the CG. Tail heavy planes are nearly impossible to control. The Nexstar is a high wing plane, so you will balance by holding the plane up by
putting a finger of each hand under each wing in the same place about 4 or 5" away from the fuselage.

Reach under the wing and feel for the spar. Should be back about 3 or 4 " from the leading edge. Check manufacturer
specs for exact distance back from the leading edge that the plane should balance. Do this with an empty fuel tand, but everything else in place, servo's, battery, etc.

Most planes fly ok if the plane is slightly nose heavy using the first spar or just a little behind it.

Check factory specs. High wing planes balance from underneath the wing. Low wing planes balance upside down on the top of the wing.

Also, check the aileron control surfaces to make sure the are set the same. You can't have one aileron partially up and the other down when the aileron and aileron trim on the transmitter is centered.

Good luck. You can find the CG specs online at the retailers website.