The online extension request form is not usually available until sometime in March. But---please explain---what are you trying to do? Why do you think you need an extension for a 1098? What kind? From a mortgage lender? 1098T from a college? 1098E for a student loan?
If you are referring to Form 1098 Mortgage Interest Statement, then yes, you can use the instructions to Form 8809 to learn about an extension of time to file it. Here is a link to the Form 8809 Application for extension of time to file Information Returns. You can file the form by mail or electronically.
If the mortgage you need to report the interest on is not associated with a business, for instance if you have a seller financed mortgage on your old home, you don't not need to file the Form 1098.