First, resize the canvas (Ctrl+Alt+C). Here, I increased the canvas size by 10CM, and then pulled out a marquee (M). Ctrl+T can directly start stretching long legs.

I want to add here that the cutting tool has the same effect as resizing the canvas.

For example, selecting the clipping tool C, and then clicking on the picture to zoom in on the picture, actually provides available space for adding long legs! The same reason and effect, but adjusting the canvas size is more accurate. )

Like this, the final effect is obvious.