VPN ports ps5

[Henioxxxxxx 0]

hey everyone, I have a problem with VPN, I don't know much about it, I would like to forward ports, I have set up VPN on the Asus RT AC 68 router with the software in Asus WRT Merlin, I have set up VPN Client, everything is fine there, e.g. a different map, my IP has changed, the problem is that the ports are still closed during the Air VPN test and when listening it shows that the ports are not open. Some time ago, someone on this forum told me to forward the ports via iptables. The problem is that I still don't know much, the information is scarce and I'm a bit lost in it. 
what would I need for this more or less what I mean is intables, I understand that it is for Linux, right?
Do I need to install Linux as an operating system to use iptables?
Can I do it in Windows 10? It doesn't matter whether I need 2 routers for this, because someone writes on the forum that I need an Asus and a Tomato, or I just need 2 routers, or will it work with just one?