If your return has been already accepted
by the IRS, you will have to file an amended return (1040X) to include the form
1099C. But you might want to wait until your refund or payment is processed.
The IRS will only accept amended returns via mail.
The 1040X form for 2018 hasn't been approved yet
by IRS. Please, keep checking the following information on how to amend your
return; it will be updated once the 2018 form is released:
https://ttlc.intuit.com/replies/3288565
