Remove the circlip to release the key cylinder. Remember, don't lose the spring and ball bearing. Now file down the back of the Concours key cylinder so that it fits into the square hole. Place some tape over the tangs of the key cylinder or else they will fall out along with the teeny-tiny spring that supports the tangs. If there is no groove left for the circlip to grab onto, then file a groove for the circlip. Once the key cylinder is in place then insert the circlip and assemble everything back together. Spray a dab of WD-40 into the key hole for good measure and test your work. If everything works and you can lock and unlock the Givi case, then you can go ahead and remove the big, red Givi key from your key chain. :-)