FAQ » unable to change rotor speed from 1150rpm

I think, it's best when you don't use the throttle channel of your transmitter. The recommended use is not to assign an channel in the calibration menu, tab functions. Then you can select the rpm by selecting one of the predefined flight conditions (key 1, 2, 3 and 4). There you can define the needed rpms.

so, you simply go to the Settings > Input Device tab, press there onto calibrate input device. Change there to functions and click onto reset in the line throttle channel.