Bowing alone may not be casing the trim problem. If the warp in the aileron is such that a part of the trailing edge is bent upward or downward, then that could be your problem as this is an unwanted deflection while the aileron is at neutral. If it really isn't warped in this fashion, then I would look at some of the other suggestions from previous posts concerning alignment or warped wing problems.

If the aileron is warped to the point it is giving you the unwanted deflection, the method of heating and reshrinking the covering may work as it does in many cases.

If it does not work, then you must take the covering off, wet the aileron (I recommend a 50 - 50 water to ammonia mix) and set it up with a twist to the opposite side of where the twist is already and block it up somehow to hold that position until the wood is completely dry. When you take the weight off, the opposite twist will spring back somewhat to hopefully a straight position. The tricky part is correctly estimating how much opposite twist is the right amount to produce the required result.

One more thought on the bowing. If the aileron hinge line is not absolutely parallel, when the aileron is attached to the wing it will appear that the aileron is bowed. It is best to make sure a solid stock aileron is straight and true to start out with.