The only answer is to remove the horizontal stabilizer and reposition it to the correct incidence (0-0). A little careful cutting with an Xacto should do it. If it can't be cut at the joint of the stabilizer you can measure below the stab a specific amount, say 1/2 inch, and place your cut at that point on both sides of the fuselage. When the stab is removed it will be easier to remove the remaining wood. The fuse can be repaired with another piece of wood and CA'd in place. It should be as good or better than the piece you removed.

Now you can reset the stab by sanding the replacement wood in place at the correct dimension.

Never assume everything on an ARF is at the correct settings. Always check before any final assembly because once you glue it, it's almost permanent until the Xacto or Zona saw comes out.

Basically what you are doing when putting together one of these models is Assembly and Rigging. It also occurs on full sized aircraft as well, when one is disassembled.