Extract the zip, then flash merged.hex from the extracted directory.
West (from an initialized nRF Connect SDK workspace with the SEGGER J-Link connected):
west flash --hex-file merged.hex --recover
nrfutil:
nrfutil device program --firmware merged.hex --recover
Use --recover on the first flash or when TF-M or credential storage must be reset. For routine re-flash during development, omit --recover if you want to keep TF-M Protected Storage credentials.
For 91m1 two-board setups, extract the bundled Serial Modem archive and flash its .hex on the nRF9151 DK before programming the host merged.hex.