Flashing firmware standalone

If none of the other methods work, there are three possibilities:

Desolder

You must remove or desolder the flash IC before you can flash it. It’s recommended to solder a socket in place of the flash IC.

When flashing the IC, always connect all input pins. If in doubt, pull /WP, /HOLD, /RESET and alike up towards Vcc.

SPI flash emulator

If you are a developer, you might want to use an EM100Pro instead, which sets the onboard flash on hold, and allows to run custom firmware. It provides a very fast development cycle without actually writing to flash.

SPI flash overwrite

It is possible to set the onboard flash on hold and use another flash chip. Connect all lines one-to-one, except /HOLD. Pull /HOLD of the soldered flash IC low, and /HOLD of your replacement flash IC high.