First, make sure the HELOC interest qualifies for a deduction. One major hurdle to deducting HELOC interest, through 2025 is the HELOC must be for the purpose of buying, building, or substantially improving your home.
If you are able to meet the all the conditions of deducting the HELOC interest, you can still enter the amount where you would have entered it, had you received a 1098. In TurboTax Online, go to Federal > Deductions & Credits > Mortgage Interest and Refinancing (Form 1098). You can add a 1098 here, and choose Change how I enter my form when you are asked to import, then Type it in myself.
See more information, including all the conditions of deducting HELOC interest here: Can I deduct interest on a home equity loan or a HELOC?