To do RC in a dream, first you must gain at least some awareness that will get you lucid or to the verge of lucidity. Then you do RC spontaneously and that either confirms what you already know or gets you that little extra nudge to lucidity.

Are you practicing any daytime awarness training? Are you doing RCs correctly during day? Those could be why you are not getting enough awareness or not doing RCs in your dreams. But that's an easy fix, no worries.