You should be able to do that using
Image > Canvas size... four times to make the four crops required, then
Tools > Create strip of images... to assemble the crops into the desired order.
Note that it is necesary to click on each image to see the full image.
For example, to convert this:

- Click to display the full image
- Before.png (7.66 KiB) Viewed 346 times
to this:

- Click to display the full image
- After.png (7.41 KiB) Viewed 346 times
Use these
Image > Canvas size... settings:

- Click to display the full image
And then these
Tools > Create strip of images... settings:

- Create strip of images.png (18.89 KiB) Viewed 346 times