You may remember from your training, the Power verus Airspeed curve. Its the one with the start at zero airspeed and power required to hover, then rises in power required until about 15 knots then falls in power required as airspeed increases to VBROC then rise again after the lowest power required point as airspeed still increases to Vne. VBROC point is also the MROD and max power available point.. .This curve is for a constant height so if the collective is stuck, hopefully not at a very high power setting, then in order to lose height you must fly either to the left or right of the VBROC/MROD point.. .I much prefer to land at a speed on the left of that point as if you must meet the ground with limited control, the slower the happier!. .Adopting a Power/Speed combination, preferably into wind for lowest G/S, with a "comfortable" rate of descent is an exercise I have often done with students.. .. .Doing turns aids in loosing height initially however diving at the ground makes slowing down difficult as when the nose is raised, up you go again.. .Takes a bit of time to get down, but it works.