@ mero_naam_ho- As damauli_guy said there is no hard and fast rule on what you write on the letter. It needs to be simple and to the point. Here is a sample if you want to use:



Name:------------
USCIS Num/Alien Num: You should have it as you have applied for EAD before.


Dear Sir/Mam,

I was granted OPT EAD on (Date if you remember) which was valid from (Start date-OPT) to (End Date OPT) after successful completion of my undergraduate/graduate( You Choose) degree. The EAD issuing office was __________( Normally its texas service center in mesquite for OPT but I might be wrong). Since, the OPT EAD has/was already expired and I am _________(working or doing further studies-Pick one whichever suits you or add what you are doing) I have misplaced it and no longer have it in my possession.

Thank You.

( SIGN HERE)
(DATE HERE)

***P.S.- I think if you write this letter it should be enough as they can pull your EAD info through your USCIS/Alien no which usually starts with "A". Hope this helps!!