Thaw your steak in the fridge(1-2 days). Allow the steak to come to room temperature covered on the counter top before cooking (about 60 minutes). This prevents the meat from being shocked when you put it on the hot surface.
A general rule of thumb is to cut the temperature down by at least 50 degrees. You can sear on medium, but then quickly move to low heat to slowly finish the cooking process. Unlike grain fed beef which requires a higher searing temperature, grass fed beef will sear on medium. The suggested internal cooking temperatures for grass fed beef is 120 - 140o Fahrenheit (which is lower than the USDAs guidelines for beef which is 145 - 175o).
Just remember, if you like your meat more on the medium to well done side, make sure you turn the heat way down to allow the meat to cook slowly. Your patience will be rewarded.