Extract the contents of the .7z file (it should be a single folder) to your Black Mesa custom folder.
If you haven't yet set up a custom folder for Black Mesa, do the following:
For a install any mod on Black mesa steam release.
- Go to your bms folder (usually located at Steam\steamapps\common\Black Mesa\bms).
- Create a new folder called "custom" (without the quotation marks) in the bms folder.
- Open the file gameinfo.txt (located also in the bms folder).
- Find the line // Black Mesa VPK files.". Below that line Create a new line and type "game+mod bms/custom/*" (without the quotation marks) in that new line.
- Save the file. Your custom folder is now set up.