Due to the questions I describe how to solder the micro on the bottom, I hope it is useful ;)
Attention!! This is not a typical build, perform these steps at your own risk, you will need to move the micro from its upper location downwards respecting the solder pins, my board is Corne Chocolate v2.1, test with a ProMicro and NRF52840.
1 Place electrical tape on the bottom side where the micro will be placed to isolate the board.

2 Pierce the tape very lightly so that the pin passes snugly, important!! you must perform the opposite side to the white mark on the plate.

3 With double contact tape place the micro, the pcbs must be tight.

4 Place the pin adjusted so that it is flush with the top side.

5 Solder the pins on the top side, the weld should be as flat as possible.

6 Cut the pin excess on the side of the micro and solder the side of the micro.

The author remixed this model.
This design don't use a screen and is designed for bottom-up build, thanks to the author for his contribution.
Update 20240919: fix usb-c compatibility test with NRF52840, remove .obj file.
Update 20240917: fix base_right and base_left files, upload .obj file.