I change it by trial and error a little at a time

I had a LT 40 back when they first came out that obviously had too much incidence for the amount of power that I had. I kept shimming the rear of the wing until I was happy.

The LT 40 has a flat stab. The Telemaster has a lifting stab which is supposed to negate the positive incidence on the wing but it doesn't completely do the job.

One good way to judge your trial and error is to watch the apparent attitude of the plane at your normal flight speed. You want the fuselage to appear level. You can adjust wing, stab, and engine thrust to achieve this.