Cut out a 2-inch wedge piece of turf in the lawn using a masonry trowel. Check your thatch layer after signs of the fungal disease has disappeared. A thatch layer over 1/2-inch thick encourages fungal diseases. If you replant over the thick thatch, your chances raise of the fungal disease returning. Rent a dethatcher if the layer of thatch is over 1/2 inch.
Dig up dead grass areas with a shovel to completely removed any fungal spores. Throw away or burn the dead grass.
Till your bare areas to break up the soil. Hand pull any weeds that may have popped up in bare areas. Weeds take advantage of bare spots and thinning grass. Prevent weeds from competing with your grass seedlings by removing them from the lawn.
Broadcast your grass seed into the bare areas. Cover with 1/8 inch of compost and water the area until it is moist.
Mow your new grass first before the rest of the lawn to reduce the risk of spreading any fungal spores left over from the disease. Avoid leaving lawn clippings on the grass until you are sure the disease has been controlled.