I'm not clear on what you mean by that letter. What should be in it and where/how do I serve it?

Edit: I think You were referring to the claim letter you mentioned in your previous post. I guess I should rephrase my question. Why is there a limit of three days? Does this letter need to be hand delivered or sent certified mail? So far the airline has told me a I have to wait until my wife returns to the USA to file a claim. She comes back to the USA the first week in February.

She bought a car seat today and, of course, got one that is too small, but now we are stuck with it because the dealer won't give her a refund. I was just informed by DL that 2 of our pieces of luggage are at Heathrow and one, most likely the car seat, is still at JFK.