Turn the garment inside out
Trim any loose threads around the hole
Place a darning mushroom, egg, or small support under the hole
Thread a needle with matching or similar thread
Knot the thread end
Stitch across the hole in one direction, making parallel rows
Stitch across the hole in the opposite direction, weaving through the first rows
Keep stitches close together to cover the gap
Secure the thread with a few small stitches
Tie off the thread
Trim excess thread
Turn the garment right side out and check the repair