How do you know the problem was too much nitrogen? What is your tomato plant looking like? What conditions was it in before and what did you do that makes you think over nitrogenated? What conditions is it in now?
Too much nitrogen leads to rapid growth of the plant with lots of light, bright green leaves, but few to no flowers. You just need to stop fertilizing it! Perhaps add a bit of potassium and phosphorus (the P and K of NPK) to balance it out. Potassium could be just burying a banana peel next to the plant or kelp meal or greensand. K could be bone meal.
But don't overdo! Nature will sort the situation out in time.... Adding compost is best, provides everything the plant needs and the plant can take what it needs.