Having fliped open lock, insert lock key and turn until you can see the brass flat pin, push with a flat screwdriver and lock barrel will come out. Insert bike key and some pins will protroud out. Either swap pins or file down edges until level with barrel casting. The pins are the same as door lock pins for old E30 3 series car so you may be able to get some spare pins from a local car dealer. They are numbered in either roman or arabic fashion, and you will likely need numbers 2 and 3 most.