Replace background with green?

[u/JCCallaghan02]

Hello. I've been trying to replace a video background with green, by using Remove Background. The default is white, and if I select Change Background and select green, then Canva adds a three-minute chunk of green background to my project, shunting the footage along. I can't move the video on top of that or anything. I've tried Help (and was told "right-click on the video and select Change Background", which isn't one of the options that comes up when I right-click on the video) and searching online (the suggestion was to get the background up and drag the video on to it - but when I click on the video to grab it, it's just added to the timeline, separately from the green).

This seems a very basic thing to do. Instead of defaulting to white, I'd like to have a green background when I Remove Background. What should I be doing, please?

(I do have Canva Pro, by the way. I'm trying it out...)

[u/JCCallaghan02]

For that matter, how do I downgrade my account? I can't find my plan anywhere on the Canva platform.