Here is a small tutorial, I think...
1. Open the image and select the Crop tool. The problem with this repeating pattern is that it's no seamless. I believe you want a seamless pattern.
![Image](http://gimpchat.com/files/6266_capture-20210910-143741.jpg)
2. Choose what square you want to use for the repeating pattern
3. Crop the square leaving out the white line that separate the patterns
![Image](http://gimpchat.com/files/6266_capture-20210910-142854.jpg)
4. Go to Filters/Map/Tile Seamless and click Ok and there you have your repeating pattern.
![Image](http://gimpchat.com/files/6266_capture-20210910-144338.jpg)
This is another image fixed