Sorry. I never finished my earlier post because our furnace started making an unholy noise. I’ve had to switch it off for the night.
Anyway…If your printer has only 1 Z-axis lead screw (obviously, on one side), then the X-axis will be held level by the wheels on the guide rails. Make sure the wheels on the X-axis on the outside of the gantry (2 on each side) are tight, but still turn freely. Once that’s done, adjust the single wheel on the inside of each side. That one uses an eccentric nut (not to be confused with people who buy 3D printers) which will adjust the grip each side has on the vertical rail. You want it tight enough that it doesn’t allow for wobble but loose enough to allow the wheels to turn with a bit of resistance (ie. you shouldn’t be able to “spin” them but you should be able to turn them with your finger without too much effort.