I AM a kid, (14) so if you don't help people like me, just say you don't, thanks.

I need help for porting forward something and I'm using this internet and a Windows 10 PC to do it. I am using this guidance: https://www.instructables.com/How-to-Setup-a-Modded-Minecraft-Server-1122/    (I'm stuck on Step 5)

I use an Archer C90(US) AC1350, and trying to get into the tplinkmodem.net website gives me the "Trying to configure the modem?" screen. I need help on trying to Port Forward the server. Is it possible to give me a simple step by step on what to do? From getting in to the website with the modem I use and how to port forward what I want? I can do the rest, but I just need a how-to on getting to the website and to the "Port Range Forwarding" section of the modem settings?