Simple X-axis levelling tool.

After printing grab a hex key (also, Allen key and Allen wrench) from your kit. Clip a Leveler at each end of your X-axis rods as shown and slide the hex key though the holes and raise or low the Z axis as needed. I start at the one closest to the Z-axis as possible. Get the hex key to gentle lay in the groove (spinning the Z-axis threaded rod as needed), now remove the hex key and slide it in the holes in the other Leveler. Now make the adjustments to the printer to get the hex key to lay in the groove like it did on the one closest to Z.  Simple!