WillC said:@Rookieplantguy - Please post a photo that shows the entire plant and its pot.
Why do you say you overwatered it?
I would just trim off the rotted part till you see good uninfected part. Apply lightly some cinnamon as fungicide on the exposed cut part. It will eventually heal and will grow new leaves below the cut off point.
Would you consider this to be uninflected? Cut off where it began to feel firm again
WillC said:The "droopy" leaves that concern you are a response to the reduced light it now gets. When grown in the greenhouse it got much more light from all sides and also overhead. In reduced light, new leaves are thinner, softer and mare naturally droopy. It doesn't mean the plant is ailing; just adapting to the change in its environment.
Rather than watering by the calendar, I suggest that you use a soil probe, such as Soil Sleuth, to determine when the soil is dry about halfway to the bottom of the pot. Under watering can be just as much a problem as overwatering.