smeash

Im not sure you can undo the damage if its badly rotted, but first step would be to dig up you plant, rinse the soil off and look to see if the roots are white and healthy, or brown or black. If you can remove some of the rotted material, and replant in a well draining mix, it may recover. Most folks recommend 50% perlite and 50% potting mix. Also the pot must drain well. Good luck!