Setting Race in a Trigger

When selecting a map as a custom game, users can select any Race they want to be or leave it on Random. But once the map is loaded, how can I make sure that they are playing as Human? Seems like a simple thing, but I can't find an Action for that.

Thanks!

its in player properties "lock player settings"
its not a trigger but it will make it so at the start they cant change there team color or race

Or you could place the starting units and create starting units melee trigger... then use a trigger to remove unused units.