Please help! Weed killer has killed my grass!

My boyfriend went to de weed the grass and it spread lots, we have loads of dead grass circles everywhere now! Its a rented property and im really worrying what the landlord will say about it when we next speak to him.
This is our first ever garden and we were really looking forward to making it pretty.
We really dont know what to do, we are trying to water it, not sure if that will actually help.
Please someone give us some advice on what to do!
Thank you

 

If you could say what specific weed killer you used and how you spread it (all over or just in spots) it might help someone come up with a suggestion.
If it's a contact rather than systemic killer there's a chance of regrowth. I accidently spilled some on a lawn and though a 'dead' patch soon appeared it eventually regenerated.

 

Did you apply a lawn weed and feed?

 

As others have said, without knowing exactly what has been used it's hard to say how to remedy the situation. If it's weed and feed you've used, it will make the grass look awful for a bit - if it's something more 'serious' once you've done what JWK suggests and diluted it, just get a box of grass seed (any cheapie one will do from Asda or Wilko etc) and sow that.

Unless your landlord makes an inspection, (in which case you just say you found some weeds in the lawn and are 'dealing with them') personally I wouldn't mention it at all. And don't worry, you'll be surprised how quickly grass seed will grow especially in this warmer weather - you can always help the process along a bit by pegging down some clear plastic over the seeded bits.