Z axis limit switch? Check if mount for Z endstop has moved/cracked and needs adjusting. If endstop mount is at lowest position possible (and endstop still doesn’t engage), then, slightly bending endstop lever arm can help microswitch to engage sooner before gantry tops out at max height. Shouldn’t need to bend endstop lever arm normally though, that smells like something else might be happening though, if still struggling sharing pic might help.
For XY squaring, there’s a few options, already seen Squaring helper ?