This would be considered a new loan, therefore you would not need to put a starting balance, you will just need to edit the 1098 entries and enter the date you took out the loan. 

However, if this line of credit was not used to substantially improve the home, you would not be able to take a deduction for the interest paid on it under the current tax laws. 

"Home equity loan interest. No matter when the indebtedness was incurred, you can no longer deduct the interest from a loan secured by your home to the extent the loan proceeds weren't used to buy, build, or substantially improve your home."https://www.irs.gov/publications/p936