Go Live in a Facebook event from your computer
There’s no option on Facebook to go live in a Facebook event via your computer like there is from Android or iOS devices, yet there is a way.
It’s pretty counter-intuitive, but you actually need to go to your own Facebook profile page and select Live Video there, as if you were posting it on your own timeline.
You will get a dialogue asking you where you want to post your live broadcast
Change it from Share on your timeline to Share in an event
This is great if you want to host virtual online events or webinars via Facebook as you can screenshare to your event.