Designing for users without meeting them

So recently I started my internship and the first thing I was told is that I probably won't meet with users (HR managers) nor do I get their feedback at least in the early stages of the design. I am designing various dashboard features one by one. As for understanding their needs and goals I created personas from LinkedIn job notices and reading couple of articles about what it means to be an HR manager. I am no UX pro, I just finished my first certificates from Interaction Design Foundation and been doing just couple of projects for my university. So I am turning to stack exchange for help.

How would you go about designing and testing without the real users?

EDIT: If someone is having a same problem as I have. I started off with competitor analysis instead, found a couple of sites and set up free accounts. Gonna see what works for them, cross check it among all the sites and choose the things they have in common. Also just talked to our Customer Care person and got some useful insights as far as pain points go.