It is often recommended that large bubbles can be fixed by drilling out the hole if the raised part is thick, or by breaking the thin skin of the bubble and filling with a piece of glass or frit.
My experience leads me to say that "drilling and filling" is hardly ever successful. There always is a mark where the fill has been made, often there is a colour variation too.
There is another possible solution for small bubbles which are at the surface but not yet burst.
Turn the whole piece over and take to just below full fuse. This will allow the bubble to begin moving to the "bottom" of the final piece. Then flip over, clean really well and take to a fire polish - quickly up from bubble squeeze temperature and with no soak - to give a smooth surface, but not allowing it to get so hot the bubble comes back to the top. This will require observation to stop the temperature rise as soon as the surface is shiny.
Small burst bubbles
Small burst bubbles can be fixed by placing small “beads” of glass made from frit in the kiln. The appropriate sized bead can be placed in the hole and others arranged in a pleasant arrangement and all taken to a tack fuse. The beads are made by cutting small squares of glass 5-6 mm and taking them to full fuse. The glass will round up at the fusing temperature and give a number of completely rounded spheres with a flat bottom.
Of course, the prevention of bubbles by inserting a bubble squeeze is the best solution.