Stack your entire LP collection on top of the warped LP. The weight of the other records will over time straighten the warped LP on the bottom.
Place the warped LP between two sheets of glass. The glass must be of equal to or larger than 15 by 15 inches. Put the LP between the two sheets of glass and store it in the sun for 10 to 15 minutes, or place it in a oven heated to 150 degrees F for 10 to 15 minutes. The sun will bake the LP and help to straighten it out.
Turn the iron to a low heat setting. Put the LP between two pieces of non-stick, clean and smooth metal. Iron over the surface of the metal. The heat will penetrate the iron and help unwarp the record underneath.