When you are in Forge, go into the editor mode. Hit start and scroll down to "Change Gametype." Hit 'A' and then scroll sideways until the gametype you want comes up. Hot 'A' again and a new round will start. Go back to the editor mode, hit 'X' and go to the last category of objects, I'm pretty sure it is titled "Objectives."
Also, there are "Starting Points" when you change the game type. It is very important you place these in the map. One more thing, the catagory is not "Objectives" it is "Goals"