You will need to purchase a new replacement overflow reservoir as shown below for about $60.
You should drain the coolant and replace it with new. But I was too lazy to remove the engine shield, so I skipped that step and tried not to spill any coolant. Grab the reservoir and wiggle it out by pulling it upward.
Replace the old reservoir with the new one and reconnect the hoses. Fill up the coolant to the Max line.