How to change transparency / opacity / color of background above and below video?

[saiq]

Hello! I'm repurposing a youtube video for instagram IGTV at a 9:16 ratio. I want to keep the horizontal video in the middle of that 9:16 box, so I can add text above and below the video. I do not want to change any effects on the actual video. I would like to be able to change the black background above and below the video to white so I can use black text. Is this possible? Thanks!

Here's a google drive link to screenshots of what I'm talking about in case that's helpful.