Previously I wrote an article about what to do before soldering the DIY keyboard. This article is also about the topic.
Prepare before soldering
Typing letters by shorting pins on the controller
After succeeding in flashing the firmware of the controller. Now next step is that I can type letters by shorting specific pins on the controller. I asked the customer support on Beekeeb, and I got the answer.
In the picture of the pinout of the controller, the way is to short the GND pin (right side) and numbers pin, for example, the "29" pin (right side 2 down of the GND) to type the letter.
When I shorted the GND with the "29" pin, I was able to type "y" x n times.
As a note, the GIPO pins mean the number pins possibly.
Caution
Beekeeb support said that the RAW pin should never be shorted to other pins. The RAW pin is also called the VBUS pin, maybe. So, please take care not to do it. In my case, I am not sure about what I did. But as I was able to type the letter and I was able to flash the firmware again for both controllers. Maybe it's time to assemble the keyboard.