Start in your gateway’s configuration section, under the OPC Server’s “Device Connections” and click on “Create new Device…”:
Select the Ethernet/IP Class1 Host Device:
Give it a name and serial number…
… and a slot number and listening address (required for external access) then “Create”:
Then, in the list of devices, pick the new device’s “More” button, and select “Configuration”:
In the “Import Configuration” section, browse to your .L5X file from RSLogix/Studio 5000 and click on “Import XML”:
Review the import on the configuration page, in the Quick Client, or in the Designer’s OPC Browser.