When i sneezed i accidentally hit my chest and it hurts. how can i reduce the pain?

Hard to know. Without an exam and possibly tests/x-rays there is no clear answer. The common first approach would be a cool compress applied to the area that may provide some relief. If it persists have it evaluated.

You can take Ibuprofen OTC 200 mg x 3 tablets every 6 hours as needed with full stomach for three days if you do not have history of stomach ulcer or kidney disease. If pain persists more than 3 days one of your ribs may crack. Adverse effect of Ibuprofen is higher if you have to take it more than 3 days so use it cautiously and consult your doctor is advised.