First, you need to boil some water. Make sure that the container you are using to soak the shirt is not made of plastic, as it might melt. A metal sauce pot is ideal. Once you have boiling water, submerge and soak the shirt, ensuring that the entire shirt is completely in the water.
Use the tongs to transfer the shirt to the washing machine. Do not use your hands, as this could result in burns. Wash the shirt in hot water using only a small amount of detergent.
Place the shirt in the dryer immediately after the washing cycle ends, and dry the garment on hot. Do not wait between the washing and dry cycling, as it allows the shirt to cool, reducing shrinkage in the dryer.
Once dry, check the size of the shirt. If it is still too big, repeat the first three steps above until the shirt reaches the size you desire.