The easy way
1. Download dan extract Yaroslav Vlasov 6-AXIS-USBCNC-GRBL
3. Find the hex file on Release folder
2. Run STMCubeProgramer
3. Flash the STM32
Remember, the default parameter is 4 AXIS.
Note :
1.the default 4-AXIS parameter is only work with USG Platform (Universal Gcode Sender)
2. For flashing the hex file you can google it, there are many tutorial about it.