This K3X0 code is shared between both the ANSI and ISO variants of both the K310 full-sized 104/105-key and K320 TKL 87/88-key keyboards.
Instructions for building the K310 and K320 firmware can be found here:
For first Flashing from initial Stock Firmware
Using dfu-util:
dfu-util --list
dfu-util --alt 0 --dfuse-address 0x08000000 --upload ${OLD_STOCK_BIN}
Using QMK Toolbox
Using dfu-util:
dfu-util --alt 0 --dfuse-address 0x08000000 --download ${NEW_QMK_BIN}
You can short Boot0 to Vdd by shorting R21 to C27 on the sides closest to the processor, as shown:
For repeating Flashing you can use BootMagic: