From the post what i have understood was.
you want RV345 to be connected to your DMZ and isolated FW for other LAN network, hope this is your Goal - if not please clarify ?
So your setup as below :
Internet --(some Router/ FW) DMZ---WAN(RV345) --Lan --PC
By Default these devices have less console config, all config to be done using GUI only
what is your network Address space for DMZ ? 192.168.1.X ? or something thing else? if that is the same you need to change your RV 345 LAN address space.
Reset RV 345 to Factory - Do not require to connect to WAN, or any network, do the basic setup of Router with your Laptop as mentioned quick startup guide, then you can change LAN IP address to different if that s Overlap with your LAN or DMZ network.