Ah....the dangers of trying to force plants to continue indoors as they have done out of doors.

First, remove it from the pot...examine the roots and tease them apart...then take some scissors or pruners and cut the plant back by 1/3....1.2.....as you choose. Remove any and all dead tissue. Clean the roots of the old soil.

Into some fresh potting soil...making sure the soil there has something below it to ensure good drainage. Shards of clay or stones or gravel...anything to keep the bottom of the soil above the bottom of the pot. I suggest the pot be at least a 6" size...but 8" will do. And I recommend clay.
If you wish, you can mix a goodly amount of sand and peat moss into the potting mix.

Make a hole and put the plant in...firm it up.
Take it to the sunniest window you have....west or south is best...east is good...north just wont do.
Water it well, until you see drainage in the saucer below.
Dump the excess...never leave water in the saucer.

Hopefully, the cutting back of the plant has generated some need for the plant to grow...that is what pruning does.

When you begin to see buds appear, you can begin feeding the geranium at 1/2 rate 20/20/20.....and increase as the amount of foliage comes.

In about 6 weeks you should see whether the plant is going to do anything....if anything.
As a couple more weeks go by, you might see the beginnings of flower buds....and then you can change to a liquid
15/30/15.....about once every 2nd water.

Hopefully your plant does come back. Each time you water, always water til drainage is seen in the saucer...then dump.
Allow the top 1" to go dry between waterings.
You might also hold the water overnight before watering the plant. This allows the water to gain room temperature.