E525W set custom paper size

How do I set custom paper size for a Dell E525W printer?

My paper is 105 x 148 mm so falls in the range of sizes supported.

I'm running Win 10 and selecting printer icon in tool bar, printing preferences.  In Paper size options, I get 20 custom sizes but they are all the same and not the size I want.

I do not see any way to set this using the menu on the printer itself.

Help!