Your question is very broad. 

Loop through all creeps in the game and you don't need to worry about rooms.

for(var name in Game.creeps) {
var creep = Game.creeps[name];
//run creep role code
}

If your question is regarding a second spawn , the above still applies.

You may however want to let creeps store their home / source room in memory when spawning.

var roomName = creep.room.name;
creep.memory.sourceRoom = roomName;