Flattening warped film

[adamadam]

I got 15 rolls developed yesterday and picked it up this morning on my way out.
However, it was in my bag all day, not kept flat, so all the film strips have the right hand side bending upwards.
I think it would be nicer flat, better for scanning also,
How do I flatten the film so that it stays FLAT?

THANKS

 

[felixcat8888]

Put 2 heavy books with the film strips between them.