This tool for Hextraction assists with leveling the game board. Put this in one of the slots, ideally top center, and put one of the balls inside. Then adjust the leveling feet until the ball stays in the center divot reliably. (or as close as you can get)

To build this tool, print the two parts as uploaded and place the tile inside the base. I would recommend gluing the tile in, but it's technically not required. I would also recommend printing at least the tile in the smallest layer height possible. Or if you have access to adaptive layers, use a small layer height on the inside surface the ball rests on. There is a very subtle curve to the surface, and a large layer height will be too coarse and will affect the ball's ability to move around with precision. It needs to be as smooth as possible, and may even benefit from some sanding.

The tile has no notches in it, so it can't be played on the main board, but the base technically could be. However, the angle would make any tile placed on it conflict with the one above it, so it's not a good idea.