Just wait- if that skin doesn't easily come off, that means it is likely still healing from an abrasion injury underneath. For now just wait- he is obviously healing & you don't want to make it worse.
Think of it like a "scab" that a person would have- you don't want to pick at it, just let it heal. When a snake has an injury, they usually shed more often as a way of healing their wound. So be patient & expect this to happen for a while.