In the Post Editor or Bookmarklet, click 'Add Media'
Then select 'My Media'
Here, you’ll see all of the videos you’ve used previously. Click the video to preview it. In the video preview, click 'Add to Post'. Then, you can customise your post as usual
How To Copy Or Duplicate A Post From Your Queue Or Past Posts
On the left sidebar in your past posts or your Queue, filter by content type to find all of your current or future videos
You can use the same video for multiple posts and different social profiles, so you don’t need to re-upload the same video. Just find any post (in your Queue, or past posts) with the video.
Click '...' to access more options and select 'Duplicate'
This will create a new post with your previous video pre-populated
