[2021] Random map in custom game?

Hey guys, want to do some match with opponents from gamebattle MLG, notice the rule say that the map must be randomize. Tried few match between friends yesterday in custom but I had to choose the map we want to play each round. Is there any option to random it? Sorry if this is dumb question, stuck in the office can't check it myself and really curious about this one. Appreciate any help. Thanks!