Thank you for your answer. I have the whole stack including the required firmware, but the tool to actually write the firmware (BittWare Toolkit Lite, including bwconfig, bwmonitor, bwdfu-programmer commands) is not included. In the past it had to be obtained from BittWare, but they no longer provide it after July 31 2020. The point is that the card first needs to be updated in a two step procedure from 1.1 (FIM version 9926ab6d-6c92-5a68-aabc-a7d84c545738, BMC firmware 26822) to 1.2 using the BittWare tools, then one can use the newer tool to upgrade it from 1.2 to 1.2.1 (i.e., to firmware version 26895, bootloader 26895).
Kind regards,
Rok