Either use the washing machine or dunk it into a tub of water.
 Or, choose another appropriately-sized chair that won't be damaged by the water.
 As it dries, the shape of the chair will stretch the t-shirt nicely for you.
Get the entire T-shirt wet.
Pull the wrung but wet shirt over the back of a dining chair.
Allow the shirt to dry.
{"src": "wikihow-all_validation", "title": "How to Stretch a Cotton T Shirt7"}