Not finding Belkin/WeMo or Sonos in my "Things"

I’m new to ST. I just installed a hub last week. I have installed a WeMo switch and plug, and connected them both to the WeMo app and tested them to work. I have also linked them to Alexa and they operate by voice command. I cannot get them to auto connect to my ST Hub by using the “Add a Thing” function, and I do not see them in the “Add Device Manually” list. In addition I do not see Sonos listed under “Speakers” in the “Add Device Manually” , even though I have seen it shown as an option in YouTube videos. Should I abandon the WeMo switches in favor of others? Any advice on getting the Sonos speakers connected?

Marketplace > things > SmartThings labs at the very bottom

Thank you very much Jimmy, that worked great. I found both the Sonos & Belkin Labs and linked my speakers and switches.