not able to get manage modem because i can't get app on PC

I have spent 5 hours trying to get my printer to work with this new Xfinity gateway they sent me.  I tried chat and they were supposed to get back to me, but that never happened.  All they tell me is I have to have the App.  I have no way of getting the App for my laptop.  I do not have a cell phone and I do not have a chromebook, so how am to manage my modem?  Why can't I manage if from the web site like we always could?  Anyone have a solution?