You can download StreamLabs Beta here: https://streamlabs.com
Streamlabs OBS app works and looks almost identical to OBS app. It has the same features. If you have tried OBS already and want to try if you will like Smartlabs OBS more, you can use the same workflow and set things identically to how you did it there.
You can also use OBS step-by-step manual to learn how to stream pre-recorded videos.
The only difference is that you have to set the streaming manualy yourself in settings > stream > paste the url and stream key "default" like always.
You then open the media and use the eye symbol to start your video after starting streaming, just like in OBS.