The private lender is not obligated to send you a Form 1098.
What exactly do you mean by a "private lender"? Is the mortgage loan from the person that you bought the home from (a seller-financed loan)? If so, enter it in the regular mortgage interest section. When you get to the screen that says "Do any of these situations apply?" select "This is a seller-financed loan and I did not receive a 1098."
If it's not a seller-financed loan, is the loan secured by your home? If not, you cannot deduct the interest. See the definition of Secured Debt in IRS Publication 936.
Mortgage interest that was not reported on Form 1098 has to be entered on Schedule A line 8b. If it's not a seller-financed loan the entry can only be made in forms mode. That means there is no way to make the entry in TurboTax Online. Forms mode is only available in the desktop TurboTax software, not in TurboTax Online.
In forms mode, enter the interest directly on Schedule A line 8b. Do not use the Home Mortgage Interest Worksheet. But when you enter it this way, TurboTax will not calculate any limits that might apply to the deduction. See "Part II. Limits on Home Mortgage Interest Deduction" in IRS Publication 936 to see if any limits apply to your deduction. If it's not a seller-financed loan you do not need the lender's Social Security number or EIN.
Whatever the situation is, keep in mind that you cannot deduct your entire mortgage payment. You can deduct only the portion of the payment that is interest.
Note that mortgage interest is an itemized deduction. It will not make any difference in your tax or your refund unless your total itemized deductions are more than your standard deduction.
You cannot claim a deduction for mortgage interest, or any other itemized deductions, in TurboTax Free Edition. You will have to upgrade to Deluxe.
