Attach a diamond-tipped masonry saw blade to the miter saw.
Position the brick properly in the saw so the marked lines for the cut line up with the saw blade.
Turn on the saw and lower it slowly. Do not force the saw blade through the brick, but allow the blade to slowly cut the material.
Blow off the brick with an air supply and air hose, to monitor the progress as the saw cuts through the brick. Attach the hose to the table, making sure the lines are out of the way of the blade, or have an assistant hold the hose properly.