First, clean off all dead leaves, and all or most of the dead roots. Then look at what you have left as far as a plant is concerned. I am assuming they are in vegging state.....

You now have the duty of matching the roots to the canopy of GOOD leaves. If there is too much green for the roots, cut more green off to give the roots a chance to be able to handle the stuff up above the water level.. You are now basically doing the same thing as when you are cloning. When you clone you cut the leaves back on the little branch so that roots will develop. The principle is the same.

SN