Not able to see a printer on the network unless...

I currently have a setup of 2 routers in my home.

One main router from my ISP that everything is connected to(Other computers,Wi-Fi printer,etc..) and TP-Link router that is connected via a Ethernet cable running from the main router into the second TP-Link router that I have my PC connected to. The second router is located in my room.

I own this setup just because the Wi-Fi signal in the house is quite bad and I wanted a Wi-Fi repeater but knew it would require a cable switch to split the Ethernet cable I have in my room for both the repeater and PC.

Looking back, maybe I should've invested in those two because my knowledge in networking is insufficient and handling 2 routers is not easy. It took me ages just to understand how to open ports because there is a process that needs to be done in both routers.

So back to the question... there is a printer in my home but I cannot access it when I'm connected through the second router, only if I unplug the Ethernet cable that is coming to my room from the main router into the second router and plug it directly into my PC it would find the printer (obviously)...

So what is the solution? Is there a way to combine those two routers? a process that might should've been done ages ago? Obviously I'm expecting a technical solution and not a physical one, I could've just gone to the store and bought a cable switch and a Wi-Fi repeater but this second router thingy is working just fine for me besides the connectivity between the two routers part.