First you need to make absolutely sure that the extra money received each year was reported as income.
Then you will enter the 1099C and it will be added to your income. It is reported in the Less Common Income section and would be considered "Personal Debt" that was forgiven.
Then due to amount already being taxed, you will need to enter an amount equal to 1099C as a negative amount, so the 1099C is essentially washed out.
To enter the negative amount after the 1099C do the following:
Go to Federal taxes
then to Wages & Income
then to Less Common Income
then to bottom to Miscellaneous Income,
then to bottom again to "Other Reportable income,
say Yes, then type Income already reported on 1099C in earlier years and enter the amount as minus (-$).
