Prerequisites:
Video or audio files need to be in the following formats to upload: m4v, mp4, mp3
How to upload a Video or Audio File
From the Events Tab set your filters to find your event that you would like to add the file to. 
Click Edit on the Desired Event:
From the Event's page select the Media Tab and select the Upload Media Button 
Once uploaded you will be able to check and update any bookmarks if required.
For more details please see the following article.
Resolve - Set and Update Bookmarks from a streamed Council Meeting