In certain cases, you may need to manually level the print bed of the Snapmaker U1. Fortunately, this is done via the firmware on the display. You need to turn a knob at each of the four corners under the bed, following the instructions. If you have trouble with the size of these knobs, you can use one of my adjustment tools, which makes the whole process a bit easier! The function is the same for all six knobs; the only difference is the grip. You can print whatever you like. I printed it with PETG, but PLA should also work fine.