To schedule a previously scheduled post at the brand level, you just have to go to your Brand Dashboard and click on the brand.
Next, go to Brand Scheduling, located on the left-side menu.
Scroll down to see your scheduling history and the post you've scheduled for later in the future.
Now hover over the post and you'll see a pencil and an 'X' icon appear on the bottom right of the post. Click on the little pencil to edit the post or just click on the 'X' to delete it.