Not something I have done for a long time. I did a big silk painting (Possibly of Asian origin) once about 30x24ish. To get it flat I dry-mounted it. Not something to do with anything of value, but this was a 'tourist' piece. I used dry-mount film pre-mounted on board. It worked fine apart from getting a hair under the silk. This is when I found out that you can peel the silk off - which I did. Thing is, once you have mounted the film firmly you have a tacky board. (I suppose nowadays you could use a ready-made sticky board). You need only give it a quick squeeze in the press at low temp. It won't bond it hard like paper, but unlike paper the fabric won't expand/contract so it will stay put. And it can be removed easily.
It's a compromise between appearance and preservation. Stick it down and lose the crease or don't stick and live with it.
My exp is that a hard cease in silk is nigh-on impossible to get out completely.