Help with Windows Network with Two Routers

I'm struggling to setup my home network using a new router I just bought, and could really use some help. The basic architecture is I have a cable model plugged into a Netgear router in my office. That is hardwired to a few devices and has an ethernet cable running to my Livingroom, plugged into a TP Link router. That router is hardwired to a few devices, and provides wifi to the house.

I managed to get everything working, except the file sharing between my Windows 7 machine in my office and my Windows 10 machine in my Livingroom no longer works. I think the way my routers are configured, they are acting like two separate networks, so Windows can't easily connect them. I want to configure the router in the Livingroom as the primary (because it's newest). Any suggestions on how I can achieve this? The old office router is running "DD-WRT v3.0-r29059", if that helps. Any help would be greatly appreciated!