Open the book to the creased page. Carefully pull back all other pages and hold them in your nondominant hand.
Place the creased page on a flat surface such as a table, floor or cutting board.
Place the non-metallic long edge of the ruler in the interior edge of the creased paper (towards the spine of the book). Tilt the ruler forward slightly.
Pull the edge of the page outward to straighten the crease. Pressing down on the ruler, drag it towards the edge of the page.
Repeat Step 4 until the crease is removed.
Repeat Steps 1 to 5 to remove the creases from each wrinkled page.