How to open ports on a TP-LINK TL-WR841ND router?

Question

WiFi

I connected an optical fiber in January, but my router does not have a connector for it, so the master installed the Rostelecom router SAGEMCOM [email protected] 5650. The speed is very low on it, so I also connected my router (TP-LINK TL-WR841ND). There was a need to open ports on both routers. I opened ports on 1 router (SAGEMCOM [email protected] 5650) via dmz, but on the second it doesn’t work, it says that the port is closed (I also opened it via dmz). Actually the question is: how to make the ports open at the same time on 2 routers?