The Typhoon H Owners Manual Version 1.2 contains this section on Accelerometer Calibration. (Typhoon H Manual Ver. 1.2 pdf)
We recommend that new owners or inexperienced flyers not use this "Hover" method. Instead, simply place the craft on a level surface (indoors is fine) and activate the Accelerometer Calibration. This can be done before or after calibrating the Gimbal.
IF you are an expert Typhoon H operator AND know how to fly without GPS, this video demos the "Hover" method. Note that this must be during no-wind conditions and in an open area.