This may have nothing to do with anything, but you should check the instructions. Some trainers come with the control surfaces in place, but not glued. You need to hit the CA hinges with some thin CA to get everthing to stick.

If the instructions say that no glue is required, that the hinges should be installed already, then it depends on the kind of hinge and how it's pulling out.

If it's a CA hinge, and there isn't any wood or anything coming with the hinge, then just deflect the rudder all the way over, and hit it with a shot of thin CA, then deflect it the other way and repeat on the other side, and you should be good to go.