1. DHCP Reservation.
2. Assign the IP in question on the PC (you didn't write it was not a PC).
As to your claim there is no documentation I'm reading the docs at https://www.netgear.com/support/product/D1500.aspx#docs
What it will NOT give is basic networking skills or training. For this discussion I will take it you know basic IP setup and skills.
OK, I don't see any mention of address reservation in the manual so for this round you have to use the full manual IP setup on your PC (AKA static IP.) For this discussion I take it you are a skilled networker, know to keep out of the IP range for the DHCP IP Pool and pause here.
As to the port forwarding, that is in the documentation so I pause here on that topic.
I've been searching for a way to assign an static IP to my computer's MAC, so I can then open a port to host a game server. I haven't been able to find any tutorial or even official documentation of my router, only generic tutorials for several netgear models that talk about options not found in my router. I also have clicked all the options in the router webpage, but found nothing. The "best" I could manage is to find an option called "Port fowarding" but after adding the port here to my current (unreliable, I would have to reconfigure it next time I connect my computer, that's why I wanted an static IP) it seemed to do nothing. Nobody could connect to the server and using an online app to check open ports says it's closed.
How can I do what I want?

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