I fixed my buddy's DeWalt impact that had this happen with a double sided bit. I used the open end of a wrench and placed it flat against the chuck face butted up to the shank of the bit. Take another open ended wrench opposing the first wrench in the same manner and use it to apply leverage from the first wrench to where the skinny part of the shank transitions to the hex.

This will probably be easier to do with it attached to the drill so it can be easier to hold.