Open the command console: ESC > Gear Icon > Under the keyboard tab select Advanced > Check off Enable Developer Console
Press the ` button to open the console and type:
map cp_dustbowl; hostname "boost"; sv_lan 0; sv_cheats 0; (I had to input this twice to be detected on my LAN for some reason)
That will create your match. Choose Scout on the Red Team.
This is a Scout achievement so the class is non negotiable. Capture all the points and this will unlock once you cap the final point.