how can i boot from a second harddrive connected via usb2.0

[bobbis]

Hello,
I have an CF-Card inside of my system, the bios is buggy and looses boot settings of a device if it is removed, so in meantime the system only boots headslees from the internal CF-Card.

Id like to know how can i boot from "boot:" or from loader promt the second harddrive connected via USB2.0.
If i am at the loader prompt from OPNsense 19.7.x the command "lsdev" only shows the internal CF-Card.. so what can i do from the second harddrive ? Thanks