Not knowing what the dress is made of (silk? taffeta? rayon? cotton? satin?), I'll stab blindly in the dark.
Wedding dresses usually have tons of extra material, either around the hems or seams or even as a part of the train, if there is one. You will need to cut some of the material from a less noticeable part and make a patch.
You will need a talented tailor or seamstress to do this. It's not for hobbyists, particularly as the cut part will also need to be sewn up and possibly reinforced so that you don't end up with another noticeable hole.
And stop smoking around your wedding gown.