The loan must have been secured by your home for the interest to be deductible. If you used an unsecured line of credit to make the improvements, the interest is not deductible.
If your loan was secured by your property and you did not receive a form 1098, you should first contact your bank to get another copy of the form. They are required to issue this form for all loans secured by real estate.
If you cannot obtain a form 1098, you can enter the amount of interest in Box 1 and select the box next to The interest amount I entered is different than what's on my 1098.You can then indicate that you did not receive a Form 1098.