This is a pretty straight-forward and reliable mechanism. If you’ve removed the honeycomb, it’s arguably better. Remove the honeycomb. Loosen the idler pulley for the Z-axis belt. Remove the belt from the 4 corner screws. Adjust the four corners to the same height (move the gantry to each location and use a fixed measure). Carefully put the belt on all four corner screws and tighten the idle pulley just enough so the belt doesn’t fall off. Double check the four corners. Tighten and lock down the idler pulley. A small fraction of a turn shouldn’t have a huge impact.
When the frame is level, then work on the honeycomb. Keep in mind that the honeycomb will likely sag in the center and you can play all kinds of games getting it level. I put a couple of shims in different places between the honeycomb and the blade/slat bed.
Also, take a look at Fine-tuning and "final" results of a 700x500mm 100W Red/Black Chinese laser - #3 by sbach72n for an idea on leveling the honeycomb.