Best papers like arches and Strathmore usually don't bend and comes back to normal flat when they dry.

For my papers which are bend I normally keep them at the end of the stack.. they get flat after couple of days due to the weight. Try that and let me know if it works for you 🙂

I usually paint on blocks so don't need to stretch. But the paper I leave it somewhere after painting might get bend coz it wasn't a flat surface.. those recover by this method 😁