1) Edit bcd_config.bat

RAWDEVICE should equal the partition device of the default boot entry in your target system's BCD
Thus, it should start with part[ or part2[ and end with two closing square brackets.
You can get it either with bcdeditmod, or with bcdedit with /raw argument present.
( remember to pass "/offline /store bcd" args too! )
If you use the latter, you will see something like:
PartEx {1b85332b-ad73-4d9a-bfc3-b39443d3dfe4} HD GPT Sig:{d2e23617-2338-4685-a2d7-f3133312e12e}
The GUIDs here are swapped in the rawdevice:
the one in gptsig[] is the FIRST guid, and the one in gpt[] is the first.

FILETOLEAK should be the path of the file to leak (by default the SYSTEM hive).
BEM is the bcdeditmod command line, should be left alone.

2) Run build_bcd.bat and ensure that it does not show any error.
If it does, then your RAWDEVICE is probably wrong.

3) Either copy the contents of the ISO directory to a FAT32-formatted USB drive,
or run build_iso.bat to create an ISO that can be burned to optical media or raw-written to USB drive.

4) Boot your target system from that USB drive or optical media.
If all goes well it should show a "loading files" progress bar, then the advanced options menu.

Choose "Disable Driver Signature Enforcement" from the advanced options menu.
If it doesn't show up then your target system has some custom CiPolicy and would require some other dumping method.

The payload should execute and dump the first sector of the file read to the screen.

The payload source is in \payload if you wish to make changes.