Are you sure the IRS is asking for an amended return? If they are holding up your first tax return, they may want a corrected form without an amendment, or they may just want you to send a missing form. What exactly did they say is wrong with the first return? And how are you going to make an amended return if you don't know the problem?
Amending appears to be available online as of 4pm EST this afternoon (March 7), but I would not amend until you have a better idea of what you are supposed to do.
