There were these at the bottom of the page Ton:
Mix 50/50 toothpaste and baking soda, rub in. Do not use gel toothpaste for this.
Rub in a paste of salt and olive oil, allow to sit for up to an hour. Wipe off.
Rub in Miracle Whip (Mayonnaise) and wipe off after an hour.
Mix 50/50 vinegar and olive oil and rub into the watermark.
Try straight toothpaste (non-gel). Rub in with the grain then wipe off.
Make a paste with baking soda and a few drops of water. Rub in then wipe off. You can also try salt instead of baking soda.
Rub some Vaseline (or other petroleum jelly) into the watermark and leave overnight. Wipe off in the morning.
I'd try on just a tiny corner of the stain first
Also it did say some people found just a hot iron without steam worked, but the steam did seem to be the key.
I'd try the vinegar and olive oil first, that sounds familiar.