How do you enter interest on home equity loan if bank does not send you a 1098?

What did you use the money from the home equity loan for? If you did not use it to "buy, build, or substantially improve" your home, you don't enter it anywhere because the interest is not tax deductible. It might be that the reason the bank did not send you a 1098 is that most home equity loans are not deductible, or perhaps they know that yours is not.

If you used the home equity loan for a substantial improvement to your home, there is a separate line on Schedule A for mortgage interest that is not reported on a Form 1098. But there is no way to enter such interest in TurboTax Online unless it's a seller-financed mortgage. You would have to switch to the CD/Download TurboTax software and make the entry in forms mode. Forms mode is only available in the CD/Download TurboTax software, not in TurboTax Online. In forms mode, you would enter the interest directly on Schedule A line 8b, without using the Home Mortgage Interest Worksheet.

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.