This guide will explain how to switch active mapgroup for specific game mode
Navigate to your configuration files section and select the config editor of your start.bat in the MapGroup field modify this to the list you require for example to switch to Gungame/Arms race use: +mapgroup mg_armsrace
default maps for specific groups can be found in the gamesmode.txt in your config section
mg_active
mg_armsrace
mg_hostage
mg_deathmatch
mg_demolition
the start map in your start.bat needs to be one of the maps listed in these groups for it to spawn the rotation on the server
Next we need to set the correct gametype/mode in your start.bat navigate to the "Game Mode:" section and for Arms Race we need to set +game_type 1 +game_mode 0
a full list of type/modes can be found here: https://developer.valvesoftware.com/wiki/Counter-Strike:_Global_Offensive/Game_Modes
* Please Note the max player slots available for each game mode

