I went to a program given by someone who was a native Chinese speaker. His “h” was heavily accented because he abruptly cut off the flow of air with his tongue. When producing “h” the mouth is open tongue relaxed and air is pushed through the vocal folds without vibration. For him accent modification would include learning how to relax the tongue while producing the “h” sound with an uninterrupted flow of air. He would need to practice at home for short periods several times every day once he was able to produce the sound correctly. The effort put in to practice directly relates to the results.