Write to a company to inform it that a certain product is defective, and that you are invoking your warranty.
To: {Name}
{Address}
{City, State, Zip}
Dear {Recipient},
I purchased {name/type of product} from {name of company} on {date}.
This product is {defective/broken/etc.} because {details of problem with product}.
According to the warranty, I am entitled to {repair/replacement/etc.}. I am requesting that {what you are asking for from the company}.
The product {is enclosed/can be shipped/etc.}. Please contact me as soon as possible to discuss the matter and/or give me further instructions.
Sincerely,
{Sender}
{Contact number}
{Address}
{City, State, Zip}