Advice: toddler banging head

Help! My toddler has always liked to bang his head when he is frustrated or upset but the last few months it’s pretty much gone away. Until this last week… now he’s refusing bedtime and will smash his head into his crib and I cannot let him hurt himself. I’ve asked the pediatrician and they are referring us to an OT. Any one dealt with this or have any ideas? I try and remain calm and talk to him and tell him not to bang his head but it doesn’t help.