IMPORTANT: Ensure you have the csgo_legacy version installed in CS2 properties.
Download the file by clicking the 'Download' button.
The downloaded file is an archive (despite .bsp extension) that can be unpacked with any archiver.
Inside will be another bsp file, and it is the actual map.
Go to Steam, right-click on Counter-Strike 2, click properties -> installed files -> overview -> Go to the csgo folder -> maps, and throw the unpacked .bsp file here.
Now, to play on this map with friends, you must invite them to the lobby, start any of the standard maps, and after loading all members of the lobby, write in the console "map soiloveplaycsgoandrg.bsp" (in your case, the name of the file will be different)..