How to rotate (already uploaded) videos in Youtube [WORKS]

Here is a short manual on how to rotate already uploaded videos in Youtube.

The original text is in italics and I have added some comments to make it more clear without italics.

Seeing how rotation has been stripped from Creator Classic, I thought this would be helpful here. I found a way to enable the native rotation buttons by modifying the element in Creator Classic.

Here are the steps:

1. Go to YouTube's Creator Classic.
 You can find it in https://studio.youtube.com/, on the left bottom as "Classic Version".
2. Go to Video Manager
Click on "Edit" on the video you want to rotate.
3. Go to Enhancements
4. Right click on the "Trim" button and choose "Inspect" from the menu that appears (do not left click)
A new window will popup highlighting the element you selected. 
This will open the source code of the website.
You should see something like:
<div class="enhance-effect" id="enhance-rotate-buttons" hidden="true">
5. Just below the line that's selected, you'll see this tag with this element: hidden="true"
6. Double click to enter edit mode.
7. Simply delete hidden="true" and press enter.

Done!

The video rotation will take a while.
If you go to Video Manager you should see that the video you have rotated appears with a label similar to "under edition.

The rotate buttons will appear and now you can use them as normal. I suspect this will no longer be possible once YouTube completely switches over to the new Creator Studio in 2019, but...works for now!

If that explanation was not detailed enough, see it in action in this quick tutorial.

This option has been disabled by Youtube, but as you have seen it is still available as to April 2, 2020. But Youtube is warning that the Creator Classic will be removed in the future, so this option will be definititely removed with it.

Original source: https://webapps.stackexchange.com/a/122365