though yours look suspiciously different! infact im gonna take a stab in the dark and say your cable has been forced down through the hole & the cable doesnt actually have a collar on it.
that looks like the cog i can see in your pic - if that is the case then you just need to retract the cog through the hole and then get the correct cable and refit.
worst case, the plastic cog falls off into the gearbox and gets smashed up by the gearbox cogs. it will not jam or damage the box, and usually draining gearbox will remove all the bits floating about in the oil!