This just happened to me, it is just an allen wrench to remove the handle. You have to remove the handle first by twisting and holding and then removing the special hex/allen screw.

I added some super glue under the washer for good measure and drilled and added the screws. There wasn’t much need for tapping, just put the screws in. I actually just put in one of them as a set screw as they were easier to find.

Thanks for the tips. I had a second hand lock fitted in the end, but it might break again.