I have one mortgage loan, in which I fill in real property tax $1,234. I also have a HELO, I fill in $1,234 again. Total tax was doubled. How to correct the mistake?

You will need to delete the property taxes from one of your mortgage loans since you entered it twice.  You can delete by editing the entries on one of your 1099 Mortgage Interest Forms.

Refer to the TurboTax Help article Where do I enter my 1098 mortgage interest statement? for navigation instructions. Select Edit by the 1098 Mortgage Interest Statement that you want to remove the duplicate property tax.