Oh my! Let's see -- probably not nearly enough light. Tomatoes can be grown indoors (see winter indoor tomato threads https://www.helpfulgardener.com/forum/vi ... oor+tomato https://www.helpfulgardener.com/forum/vi ... oor+tomato
) but it is not easy. When applestar does it, she grows selected varieties that are early maturing, handle less light, are dwarf, etc. AND she gives them artificial light as well as the window. Tomatoes are full sun plants that require a good deal of help to grow indoors.
And yes almost certainly over-watered. You don't want them to dry out, but you don't want their soil soggy or for them to be sitting in water in that saucer.
And you don't have one tomato plant. It looks like four stuffed into one tiny pot.
That's a picture taken from one of those indoor tomato threads. That is one dwarf tomato plant in the white container. Gives you some idea of container size.
So I would repot in a good organic potting mix, giving each plant its own larger pot. Bury them deeper than they are now, so a lot of that bare stem is underground. Tomatoes have the unusual property of being able to grow roots from stem that is buried, so that will increase their root system. Get a lamp to shine directly on them from just a few inches away. What has worked for me is having a table next to the window with the plants on it and then one of these
multi-headed floor lamp with the lamps on flexible goosenecks so they can be individually aimed. Keep it on sixteen hours a day.
After repotting, don't fertilize until the plants are putting out new growth.