DMZ - Setup

I would like to have one of my PC accessible from outside. So I am planning to put 1 pc in DMZ. Now in order ro minimize risk, I had setup guest-wifi on my verizon fios router and connected this pc on guest-wifi.

If I go in DMZ setting it only allows me to add ip for 198.168.1.XXX but on guest-wifi nextwork i have 192.168.200.XXX

Can somebody please guide how can I have a PC on guest wifi network in DMZ or my basic need is to have a PC accessible from outside?

Thanks