Beforehand, you must start the vario without the sdcard, then connect it to the PC via the USB socket. It will be recognized by the PC as a COMx serial interface (example: COM4).
Now launch the Arduino IDE and open the sketch you want to compile. For example, the sketch Gnuvario-E.ino.
In the Tools menu, make sure you choose the right card. The most classic of this project is the ESP32 Dev Module.
and select partition scheme: Minimal SPIFFS (1.9 MB APP with OTA / 180 KB SPIFFS)
Still in the Tools menu, choose the serial port corresponding to the vario.
You must now choose the screen / PCB combination that you have.
To do this, open with a text editor, for exemple Notepad ++, the file HardwareConfig.h located in the folder Arduino\libraries\HardwareConfig.
The choice of the combination is made by uncommenting the line corresponding to your combination. Here version 293.
Save the file then go back to the Arduino IDE.
Now all you need to do is click on the upload button.
This will start the compilation of the code, then update the vario. The vario will restart on its own at the end of the procedure.
You can now unplug the USB cable and stop the vario.