If I refinanced my mortgage with another lender in 2019 and the interest paid to the prior lender was under $600 so no 1098 - how does that get entered?

Just enter everything when prompted as though you have a 1098 Mortgage Interest form.

• You’ll be entering the equivalent of the amounts from the different numbered boxes of the 1098 Mortgage Interest Form without actually having that form. 

To enter your 1098 Mortgage Interest form, see Where do I enter my 1098 mortgage interest statement?