I suggest you read the rclone documentation, it explains how to use rclone. But in summary you just set up your remotes, and tell rclone to sync to/from/between them.
Not sure, but you really don’t need to. Instead use rclone as suggested before. That’s the right tool for syncing with Backblaze. My suggestion with rsync was on a more general note, for when you need to sync files. It’s a really good tool, but if it isn’t made to work with your specific source/destination then you’ll have to use a more specialized one such as rclone. Sorry about the confusion there.