If a plant starts to show symptoms of over-watering, first check that the drainage hole in the pot is not clogged. If it is, unblock it and don’t water for a few days. If you can’t unblock it easily, remove the root ball from the pot, and improve its drainage by placing gravel, ceramic pieces, stones… at the bottom of the pot. Then return the root ball to its place. Do not water for a few days.
If it is not obstructed and has already lost part of its leaves, you can try to recover the plant by carefully removing the root ball from the pot, wrapping it in several layers of absorbent kitchen paper, and leave it so for 24 hours. If the leaves get soaked, add new ones. Then put the plant back in the pot and don’t water it for several days.