You need to ask yourself some questions before attempting to de-enamel the piece. De-enameling is NOT without risks. Did the enamel come out really badly (as in pitted, burnt, bubbled.) or is it just that you didn't get exactly what you were expecting? If it's the latter, my advice is "Learn to love what you got".
Enameling is a constant source of surprises and "design opportunities" (as opposed to "Mistakes"). It's a good idea to embrace the unexpected. Remember, others looking at the piece won't know what was in your head when you made it and will judge it differently than you will. We often focus on "what we didn't get" and lose sight of some of the beautiful things we DID get because of that.
Here's the thing with De-enameling. It's not a cost-free eraser. It's not like you can keep applying enamel and taking it off until it's perfect with no side-effects. When I put the de-enameling section in my book Enameling on Metal Clay: Innovative Jewelry Projects, I did so thinking it was understood that de-enameling is a course of last resort, something to do when the alternative is tossing the piece in the recycle bin; but now I'm finding people are using it if they are only slightly less than satisfied with their results and that wasn't how it was intended.
Once you de-enamel a piece the surface may become coarse and pitted. Also,
attempts to re-enamel may result in the enamel pulling or failing to adhere to the silver. In order to improve re-enameling results, the piece should be completely re-fired without enamel using a high temp firing sequence (1600 for 10 minutes or so). If any black marks appear after this firing, try removing them with a wire brush and/or pickling the piece. If neither of those methods work, hit it with the de-enameling formula again and refire it again. The piece must be clean and free of both enamel and the de-enameling agent before attempting to re-enamel it. Once it's clean it needs to be well burnished. Tumbling for a minimum of 2 hours is a good choice. If you are enameling smooth areas, get in there with a burnisher too.
Here's the instructions for de-enameling:
Mix equal parts table salt and Cream of Tartar. Add just enough water to make a thick paste. Apply the paste to the enamel, coating it very thickly. Put the piece on an old piece of sheet mica (you won't be reusing this mica for enameling. Keep it aside for de-enameling only) and place it in the kiln at 1450 for 2 minutes. The mixture will burn, smoke and blacken. After you pull it out of the kiln, while it's still glowing hot, drop it into a bucket of cold water. Use a wire brush to remove the de-enameling residue. If the enamel is very thick you may have to repeat this procedure more than once.