Shrinking elastic material

I have some straps for bike rear carriers (Dutch bikes) which have become over stretched.

Now I remember in the old days that belt drive turntables used to suffer from stretched belts, and a fix was to put the belt in boiling water so that it shrank back to the original size.

I have Googled without much success; well

So has anyone shrunk elsticated fabric by putting it in very hot water?

I am looking to shrink the fabric back to the original length and restore the elasticity if possible.

Cheers

Dave R