Seedleranswered grow question 9 months ago i would say you made the fatal mistake of overwatering! its true you have to keep them somewhat moist but the roots also need oxygen to breathe and they can't do that, if everything surrounded by roots is wet, they will drown and rot.
we all made this mistake at least once so dw, that happened but im truly sorry, i know it can be heartbreaking. seedlings need not a lot of water just high humidity.
get yourself a new bean and start again and this time maybe just water with 2-4 bottlecaps of water carefully so the soil got some water and the roots can stretch out searching for more water.
i would reccomend a Youtube video on watering, this should help the most! keep on trying!