It does not make much sense that the IRS would want you to just send the same amended return again with no changes at all if they accepted your Form 1040X already. Better re-read the letter and see if they are requesting copies of any tax documents that changed your refund---what did you change? Did you add a W-2 or some kind of 1099? Are they asking you to send copies of those documents with the 1040X?
That being said, in order to re-send it, you will need to print it, sign and date it, and mail it in. You cannot e-file it again.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**