Looks like root rot or stem rot? Alocasia plants are tuberous, that means they sprout from a central rhizome. Because of this, it's not really suitable for propagation by means of taking cuttings. You can try to stick it in new soil but I don't think it will help much. Give it a try, cut off as much of the mushy stuff as you can until you hit healthy tissue and put it in soil and see it you can get roots again. The problem is from keeping the soil too wet and cutting off the oxygen from the roots. .