Install the printed spacer between the track and the wood. Make sure the small lip on the spacer is on the flat outside edge of the track (arrow). Reinstall the drawer and check functionality.

While checking final functionality watch for: difficulty pulling out the drawer (remove spacer width), falling out of the track (add spacer width), and misalignment with other drawer facings (add or subtract spacer width on each end)

*Added Bonus: If you print multiple spacer widths you can adjust, per millimeter, a misaligned front drawer face to align with the drawers above or below it. Do this after the drawer functions correctly using the spacers.