Another way to loosen up your plantar fascia is to use a tennis ball or golf ball (golf ball is deeper). You can also use a frozen water ball to apply ice at the same time, or even a rolling pin or can from your kitchen.
Seated, place the item under your foot and slowly roll the bottom of your foot over the item.
Try to think of lengthening the area between the balls of your toes and your heels - like you would lengthen dough with a rolling pin