It’s in the FAQ…
FAQ: WIFI Devices in ST? How can I integrate a WiFi or Bluetooth device that isn’t listed in the SmartThings app? FAQ
Is there any way to get WIFI devices, such as a plug, to list in ST? I currently have 3 WIFI plugs that are running off Alexa, but I would like to get them into ST somehow so I can include them in my automations, plus it would be nice to have everything in one place and feed to my ActionTiles. Thank you.