Prerequisites

STM32 programming software: https://www.st.com/en/development-tools/stm32cubeprog.html

Latest Release of SympleAF Firmware: https://github.com/AlistairSymonds/SympleAstroFocus/releases

An STM32 programmer (Such a cheap ST-LINKv2)

Connect the VCC, GND, SWCLK and SWDIO pins of the STLINK to the corresponding pins of your PCB. Then ensure the programmer is connected to your computer's USB and open up the STM32Cube Programmer Software.

Using the STM32 programmer app, follow these steps (locations labelled above)

1. Select the "Erasing & programming" tab from the bar at the left
2. Connect to the ST LINK programmer at the top right (You may need to update the STLINK's firmware, just follow instructions presented)
3. Browse to the downloaded firmware file
4. Select verify after programming - ensure the other two options are unchecked.
5. Click the start programming button and after a few seconds you should see a green success message in the bottom console.