Transforming an image?

[Knusbrich]

First of all, I would like to mention that I am an absolute beginner in using GIMP.

I have a picture of a fence photographed from a drone. The fence looks like an ellipse in the picture, but in reality the fence is square. I have studied various videos on Youtube, but have not found one that helps me further. I imagine a kind of free transform tool where you can push and pull the frame of the picture in different places, so that the fence becomes more square. In short, it is described as changing an ellipse to a square. Does anyone have a link to a tutorial or a plugin that can help with this task?

[Ofnuts]

If the drone isn't at the center of the fence, you get perspective distortion (the side of the fence farther from the drone is smaller, so a rectangle looks like a trapeze. This is fixable with the Perspective tool in "Corrective" mode.

If the fence looks like an ellipse, the drone must have some kind if fish-eye lens. You can try to compensate this with Filters > Distorts > Lens distortion.