From GRA

You left the United States and are still in possession of the I-94 or I-94W forms!

Then it is in your best interest to forward it to the appropriate authorities so that your record is corrected and that you do not experience any problems on future travel to the United States as a result.

Here is the process that you have to follow:

• It is very important that you complete the back of the card listing:

The port of departure
The date of departure from the United States
And the carrier/flight information.

• Send the

*I-94 or I-94W form
*Together with a letter of explanation
*And an evidence of your departure from the U.S. (For instance the original boarding passes you used to depart the United States) 

• Send all those documents to:

DHS-CBP SBU, 1084 South Laurel Road
London, Kentucky 40744
USA 

That's it you're all set!

If you are looking for more information on the I-94 or I-94W forms, follow this link!!!

Or this one, if you'd like to know how to get confirmation that your I-94 or I-94W was received by ACS!!!