Keep about 3 inches of the bottom of the celery and poke it with through with sticks then place it in a bowl of water. You’ll want to keep the celery’s roots from touching the base for better growth. Put the plant in ample sunlight.
You should see some regrowth in the centre of the base in about 1 – 2 weeks. When that happens you can move it to a soil-filled pot. Keep the soil damp and water twice a day.