For Android users, open camera by clicking + plus available in bottom menu. On the left side of the record button (in red) you will find a video 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, click on the + plus icon available in the bottom menu and then select edit video. A new tab will open 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.