Lightly mist the crease with water from a spray bottle. Do not soak it. Place something heavy on top of it such as a large book or small piece of furniture and leave it overnight. If the crease is still there, mist it again and repeat.
Lay the rug outside in the sunshine or hang it from a clothesline. Let the sunshine remove the crease for you.
Place a towel over the crease and iron it out. Set the iron on the lowest setting.
Place the rug in the bathroom while a hot shower is running. The steam will help to get the crease out.
Tape the rug with carpet tape. Pull the ends taut and secure them with the tape at all corners and in the middle. This will help to stretch the crease out.