I wouldn't recommend ironing BO material usually it has been treated with an acrylic coating that wont enjoy high temperature

if you do then use a cool iron over a damp tea towel as you mention.
As PJ mentions, any light creases will pull out nicely once you have it fixed over the frame, just make sure you work from one side then over to the opposite then back again etc pulling the material taught.
For heavier creases I'd probably bin it or take it back to the shop (alternatively use it for whats its made for in the first place, blacking out windows

) and get some more, ask them to roll the facric and not fold it!
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