Tension the line

Start at the highest point at the arm with the double hole, tie a knot in the line to keep it secure, then with the dryer fully open work along the line pulling the line tight as you go and feeding the slack line through all the way to the lowest point.

At the lowest point when the line is tight mark the point in the line where you need to tie the knot, now close the dryer so the line is slack and tie the knot, when you open the dryer again the line should be tight.