For Android users, open camera by clicking + plus available in bottom menu. On the right side of the record button (in red) you will find an image button which when clicked opens up a new tab showing all the videos on your phone. Select the videos which you wish to upload and click next to edit the video, add filters, and then upload it.
For iOS users, we don’t have this feature yet in iOS. We are working on it and will be available soon.