Removing router bit that is stuck with damaged shaft
While the other answer is correct in normal conditions - that is the purpose of the pin.
I would use a bar that fits into the hole in that shaft and a properly fitting wrench as if it has been overtightened it will need some force to undo it.
Using the normal mechanism relies on the strength of the aluminum casting which may break under these conditions. And looking at the first picture it looks as if that casting is already cracked so take care.