1. Open the portrait photo with PS software on the computer, and then click the "image/rotate canvas" option in turn to rotate the picture to a proper angle.
2. Then click the file menu in the software to create a new canvas, and enter the size of the final image output in the canvas.
3. Then select the move tool in the toolbox and drag the picture onto the newly created canvas.
4. In the new canvas, you can deform the picture by pressing the shortcut key "CTRL+T", and then adjust the picture to fill the canvas. However, this method may cause the picture to be a little deformed when filling.
5. When the picture is not allowed to deform, you can press the shortcut key "CTRL+T", and then press and hold the shift key of the keyboard to zoom in and out the picture to a suitable position.
6. Then click the imitation stamp tool in the toolbox, press the alt key of the keyboard, select the fill color in the picture area near the blank, and then fill it carefully to eliminate the blank area.
7. Constantly fill and modify the picture, and finally you can get a good horizontal picture. After completing the above settings, you can change the portrait photo into a landscape photo.