M.C.
Give him an alternative to headbutting and give him words to express his dissatisfaction. "You are frustrated because the blocks keep falling down" and show him how to blow out hard or squeeze his hands together really hard as an alternative. This will take a long time, but keep talking using words like frustrated, angry, upset, tired, etc. to help him identify his feelings. it is really easy for him to express himself by headbutting, so it will take time for him to develop these new skills of using words and squeezing or blowing. Repetition is key. Good luck.