If you've got a new one have a look through the handbook or email Ifor Williams. Certainly the version I have uses an Allen key externally but you must make sure it is a key that will fit as they come in different sizes. I carry an Allen key in the car always.
Any suitable bar screw driver wheel wrench, put in ring and turn, also make sure breast bars are right way, believe hung in centre so pin bit goes on outside.
Spooky to see this I have just had to use my Allen key this morning very very frightening experiance .
I saw a new IW at the hounds last week the owner had strapped a pair of pointy nosed pliers to the side I assume that's what they where for .