Connect router to PC, as if it were the ISP of the router [duplicate]

I’m very new to networking and especially the Hardwere part of the networks, but I started working on something for which I don’t have enough knowledge, but hopefully this is an opportunity to learn. Is it possible to connect a PC to a router, but not in the usual way. What I mean by this is instead of connecting the router to the PC in a way that the router gives internet access to the PC, I want to somehow connect them the other way around. I want to connect the router in such a way that the PC gives network access to the router that then spreads it trough wi-fi. In other words, I want to make the router think that the PC connected to it is its ISP. So this PC will act like an ISP for the router, giving it an IP in the context of this closed network. Intuitively, I connected the WAN port to the PC, instead of the LAN one, but I don’t know how to interact with it. I guess I need high level access to the firmwere of the router. Now, I want to mention that hopefully, this question made you understand what I’m trying to achieve and I hope someone point me in the right direction.