I found this, it may help:
In this case, I am printing on a 4x6" label printer. I leave everything formatted as 8.5x11 and then go to print. I changed the print option to the paper handling section, check the scale to fit paper size box. And then change the destination paper size to the one I want. If you scroll to the bottom of the list you should be able to find your custom size.
Warranted, this is biggest failure of office 2016 and this solution is the most techneck i have seen in a while. But, it worked for me, so hopefully it helps you and any body else that stumbles into this solution.