Adding limestone to areas of the lawn where there is discolouration due to pet urine has been known to help. You should remove dead grass as much as possible. Apply a light layer of Hi-Yield Agricultural Limestone to those areas directly and water in. Wait about 7-10 days and add fresh soil and then you can reseed or resod the areas. 

Hi-Yield Agricultural Limestone is applied at the rate of 4-5 lb. per 100 sq. ft or 40-50 lbs per 1000 sqft and no spreader will have that high setting.  This product is typically dumped on and spread thin or applied over multiple applications over a few weeks to equal the correct rate, ie 10 lbs per 1000 sqft for 5 weeks for 50lb/1000   Unfortunately, we do not have the spreader settings for that specific combo, and since the manufacturer does not list that spreader on their bag we are unsure what the exact setting would be. Due to the thousands of granules on the market and just as many different types of spreaders, there isn't a master list that exists. You may want to try calling the manufacturer of your spreader or the chemical itself directly, to see if anyone on their staff has that info. Otherwise, you will want to calibrate your spreader to the product you are using and its application rates. You can see a short video on how to accomplish this here.