Corners, How do I sew in Gimp?

[AngelH]

Googling my question hasn't given me the answer so I'm wording it differently here.

I want to take a rectangular border.
Transform one by 90 degrees.
Have them meet in the corner.
But then I want the border to look like a border made into a frame.

In other words for those who sew I want it to look like the preview image for this video,
https://www.youtube.com/watch?v=o3twJCHAQfI

But of course with my digital border.
Does anyone know how to do this?

Thank you,
Angel