The effects of dog urine on your lawn are similar to that of a nitrogen-rich liquid fertiliser. A little fertiliser makes your lawn healthy, but too much will kill it.
Pouring or spraying water on the area after your dog urinates will help to dilute the urine and lessen the effects of the nitrogen on your lawn.
The more your dog drinks, the less nitrogen will be concentrated in the urine and the less damaging it will be to the lawn. It will also be healthier for your dog.
Some products are impregnated with pheromones to encourage your dog to pee on or near them. Designating an area for your dog to urinate will save the rest of your garden.
Fertilised lawns may already have as much nitrogen as they can handle. Even the small amount of nitrogen in dog urine may be all that is needed to burn the lawn.
There are a number of products available over the internet. Spray product on affected areas and flush with water. If the treatment doesn't work then you will need to reseed the damaged area.