Port forwarding no more new router exactly the same

Tech came out to see why pops couldn't get 2160p channels

Traded three boxes got my uh DVR box to come by mail so pops can enable 4k hopeful. One box being my router even though same exact model

I head into the router page and now forces me to use this crummy site which knew+stored all my ports from the last router and insists still in use when not, my ipv4 changed I try to delete even the devices by ipv4 that don't exist no more (since constant re-assigning ipv4s) and does not budge

Can I assign my PC's ipv4 so all these things just carry over?

My router page still allows me to use DMZ (Dreamcast really needs that.), so why can't I continue my port forwarding needs directly through the router instead of this whiny middleman garbage?