The feed has burnt the grass so the only thing that you can do is to water the lawn regularly and the grass will grow back. Then don't have the mower blades too low for a while after the new grass begins to grow.

We did this once. Next time you need to take care to spread the recommended amount very evenly.

Many lawn feeds are hazardous to the lawn if there is insufficient water after application, also. If there is only light rainfall, then the hosepipe is essential, preferably used with a sprinkler that can be set on the lawn and run for a half hour or so. It's hard to apply sufficient water by standing there, waving the hose around, with the thumb over the end! :)