Cigarette burns are bound to happen if you are a smoker or even if you live with a smoker. It's possible to repair a cigarette burn in leather if you choose not to use a professional service.
Cut a small circle out of the cardboard. The circle should be slightly bigger than the cigarette burn hole. Insert this piece of cardboard into the hole, making sure it is not too big. You may have to try cutting out different sizes before finding the one that fits best.
Pinch up the leather at the side of the hole if necessary and put the cardboard in at an upright position to avoid further damaging the leather. Make sure to use scissors to trim any edges that are burned. What you should be left with is the hole with the cardboard showing through.
Cut the leather piece to size. The size you cut should be slightly bigger than the hole itself. If you are limited on the amount of matching leather you have, cut too big first and trim once you try it. Keep placing it on the hole until you have it at a suitable size.
Apply fabric glue to the piece of patch leather. Use a generous amount, but be careful to make sure it's not so much that it builds up at the edges. Fabric glue is thick and strong, so do not assume you will be able to remove all of the excess glue once it dries.
Allow the glue to dry thoroughly. If possible, place a heavy object such as a book on the patch. Follow the drying guidelines on the label of the fabric glue that you use. If you are repairing furniture or a car seat, make sure that no one uses it until the glue is completely dry.
Trim off any excess leather after the allotted drying time has passed. Make sure the scissors are small and very sharp to allow for a clean line around the patch you created.