Form 1098 would be reported to as a tax deduction for the mortgage interest you paid to the new lender. This is reported in TurboTax in the Federal > Deductions & Credits section of your return, scroll down to Your Home and click Revisit/Start next to Mortgage Interest and Refinancing (Form 1098) section.
Your new lender may also have issued a 1099-INT to record interest paid to you. This is income and must be reported on your return. They may have paid you interest if they hold money for you in escrow to pay your property taxes and insurance. This should be a relatively small amount. You would report this in Federal > Wages & Income > Interest and Dividends > Interest on 1099-INT.
If you received a 1099-INT from your former seller-financed loan, as others have said, that may be sent in error and you will have to resolve that with the issuer.
