Report to whom? The IRS? The Bankruptcy Court?

Sorry, to the IRS with an amended return. I received a late 1099-C.

This is practically an impossible call really. Is the debt forgiven related to the bankruptcy? What kind of forgiven debt is the 1099-C for? Credit card debt? Foreclosure on real estate? Something else? most importantly, in the 1099-C a tax year "2018" 1099-C? Or some other tax year?

The 1099-C is supposed to be issued as of the date of a qualifying event that makes the debt uncollectible.  If this debt was discharged in bankruptcy that was final/closed in 2012, then that was presumably the date.  (If it was a reorganization bankruptcy, things may be more complicated.)

But that just means this was 2012 income, and if you amend to report it in 2012, you will owe tax plus late penalties and interest.  Not reporting it at all might get you off (since 2012 is past the audit deadline) or it might get you in front of the Tax Court.  It’s not a simple situation.  

It also depends on what the debt was.  There are special rules for foreclosure of your main home where you lived.