Now use the clamp again to hold the iron upright and upside down. Switch the iron on and wait for a minute or two until the right temperature is reached. I set mine to ‘Silk’. Then insert the book into the cover and rest the whole package, spine down, on the sole plate. You need to experiment to find the right heating time. With my iron it is about 30 seconds. If the sole plate is slightly smaller than the spine's length, shuffle the book to and fro a little so the ends are heated as well. You will usually see hot glue exuding at the ends of the spine, and this is an indication that it is time to stop heating. Do not heat the glue for too long so that it starts running everywhere. Also, take care not to get any glue on the outer surface of the cover.
You also need to take great care when removing the book from the iron. You must not disturb it in the cover at all while the glue is still soft. Keep the cover and book block firmly pinched between your fingers as you move the package from the iron and lay it flat on your work surface. Prepare a section of your table beforehand where you can lay the book down and leave it to cool for at least fifteen minutes.