You probably have a wifi router, connected by copper between PLC and Router.
You need to have a fixed IP on the port on the router that is connected to the PLC.
This IP must be reachable by the PLC. F.ex. Router=20.1.1.1, PLC=20.1.1.2. Subnet=255.255.255.0
On the PLC, the Routers IP (10.1.1.1) must be set as the Router/Gateway in the HW Config.
That is all.