You can do this a few different ways. If there was not living portion of the tree above the ground, and all new growth is from the base of the trunk, and you want a bush shape, I would think out all but 3-4-5 of the shoots and let them develop for the rest of the season.
If you want a tree shape, I would remove all but the one that you want to form your new trunk, and let the energy be directed to the one shoot that will be your new trunk.
If heat and sun are excessive (say in Phoenix, AZ), you can paint the trunk/shoots white with a mixture of 50% water and 50% LATEX (water-based) paint. Do NOT use oil-based paint. You can also wrap, loosely, with white paper to shade the bark. Both are commonly dne with planting of new fruit trees (citrus, stone fruits, etc).
If you have new shoots at the bottom, and new growth further up the old trunk, I would do essentially the same thing. If you want a bush, remove what doesn't contribute to the shape you want. If you want a tree, prune off what is not in keeping with the desired shape.
I would have done this earlier in the season, but it can be done now, with proper care against sunburn, or you could wait till dormancy, and do it then. You still have the problem of protecting this year's growth from damage next winter, however you decide to proceed. If it is allowed to die back again this coming winter, you will just need to repeat the process all over again,