"iron in"

[pink dragon]

Sleep on your back. When you sleep on your side or front， you bury your face in the pillow， 'ironing in' the wrinkles.

I can't find "iron in" in dictionaries.
But "ironing out" means "removing the creases" and "in" should be the opposite of "out", so it's like "making wrinkles", isn't it?

[Anglika]

Not far off. It's saying that by sleeping on your face, the pressure of your head means the wrinkles in your skin will become set. It is a metaphorical use of "iron in".

[pink dragon]

What is the non-metaphorical meaning of "iron in"?
I can't find any dictionaries that have it.

[Anglika]

"When you have finished making the dress, you must iron in the pleats so that they keep their shape."

"The darts in the bodice must be ironed in before you proceed to inserting the sleeves".

[pink dragon]

Thank you very much!!!
Native speakers are realy helpful when we come across expressions which can't be found in dictionaries.