Familiarize yourself with the basics of Firmware configuration.
Download the latest OATFWGUI version, unpack and launch it. Go to the OAT online configuration tool and go through the steps for the OpenAstroExplorer. Download the local config and save the .hpp file to the OATFWGUI folder.
In OATFWGUI select develop as the firmware version and press download. Select OAE Board v1 as the board. Select the local config you have generated above. Press Build FW and wait for it to finish.
Connect the ESP32 to your PC. It can not be connected through the OAE PCB, it has to be connected to the USB Port on the ESP32. Select the proper port, then press Upload FW. When the console shows the Connecting....., press and hold the boot button on the ESP. Release when the console switches to Uploading.
You can use the online configuration tool to generate a local configuration file.
Refer to this local config and upload the firmware through VScode and Pio until those tools have been updated. This config assumes the hardware from the BOM, so a 0.9° RA Stepper, 1.8° DEC stepper with 50:1 wormgear and 28BYJ-48 steppers for ALT and AZ, aswell as the OAE board with an ESP32 and TMC2209 drivers for RA/DEC and A4988 drivers for ALT/AZ.
Download the oae-fw branch from the Firmware Github.
The necessary steps can be found here.
Flash the firmware with the oaeboardv1 environment.