Singer 6038 Instruction Book page 74

5. Set stitch width to the first mark. Carefully turn the
hand wheel to observe if the needle will enter both
holes of the button without striking the button. Adjust
stitch width or the button/fabric as needed (illustration
3).
6. In this position, take a couple of stitches (illustration 4).
7. To fasten stitching, turn the hand wheel again until the
needle is out of the fabric, adjust the stitch width for
straight stitch position and make a couple of more
stitches.
8. For 4-holes buttons, repeat the operation with the other
2 holes.