On the vertical lock, on the left side of the machine where the laser plugs in, a small vertical arm is pulled forward to engage the teeth of the horizontal cog. The six sided small post that supports this arm cannot turn but there is a tiny bit of forward and back play. With a Phillips screw driver slightly loosen the screw under this post. A mirror is useful to do this. Once loose, hold the post more tightly against the cog and then tighten again. For the arm to fully enter the gap between the teeth, this adjustment is very easy to do. Bear in mind that a heavy hand can slide the whole machine along the runners despite the lock, so rather than hold the control handles, push with one hand on the U part of the handle or actually push the machine base, which avoids any opposing pressure. Happy quilting.
