If you have located a hole in your down comforter, you need to repair it right away. Allowing a hole to remain in a down comforter may lead to feathers flying out or insects getting in. Use fabric glue used to repair seams to patch small holes. Patch large holes with fabric glue and a swatch of fabric.
Squeeze fabric glue around the edges of a small hole and bring the sides together. Allow the glue to dry.
Cut a small swatch of fabric in a square or other shape, preferably in the same color family as the down comforter. Glue the swatch directly over the hole using fabric glue. Allow the glue to dry.
Iron on a patch of cloth using iron-on fusing tape, which you can purchase from a local craft store. Follow the instructions on the package, which basically require that you press an iron on the tape to attach it to the patch. Remove the adhesive backing and iron the patch directly on the comforter. Do not press the iron longer than instructed on the package, or the adhesive will lose its stickiness.