There is no need to adjust the trim for landing.

When you decide to land, you reduce the throttle. This will cause the plane to slow down and therefore, lose altitude. The plane will assume a slight nose-down attitude to maintain flying speed.

The trick is to reduce your power at a point where you meet the ground while you are over the runway.

If you are too high, you'll have to go around. If you are too low, you'll need to increase throttle to make it over the threshold.