I'm not sure that amending a return for $12 would result in additional taxes owed. You might want to start the amend process to add it and see. That said, the IRS will likely catch it and, if taxes are owed, they will send you a bill for the additional amount of taxes plus interest. The taxes plus interest will likely only be a couple of dollars, if anything is actually owed.
------------------
Here are details on Amending
Once your return has been submitted for e-file,
you cannot make any changes until it is either Accepted or Rejected. The
IRS will not receive the change.
Then, when/if the Return is accepted, you will file a new
amended return. If your return is Rejected, you can go ahead
and make the change and then resubmit the e-file.
Amending is done on Form 1040X. That form should
be available for amending 2015 returns mid-February. Also, if your
return is accepted, you should not try to amend your return until it has been
fully processed and you have received your refund or your payment has cleared.
Amended returns have to be printed and filed by mail. It
can take the IRS up to 12 weeks or longer to process them. If you are
due a larger refund than on your original return, your amended return should
only show the difference and you will receive a separate check for it. If
you owe money on your amended return, it will show only the new amount owed,
you will have to mail a check with the return.
How to Amend?
https://ttlc.intuit.com/replies/3288565
