I don't understand what you mean. I use the right mouse button to increase the Altitude setting, and the left mouse button to decrease it (while holding the mouse pointer over the knob).

To get the L-1011 to change altitude, you need to use the VS button on the AP, and set the descent rate. You also need to press the ARM button above the altitude, so that it will stop descending at the new altitude you have set. This also applies if you want to increase the altitude.