Hi. There is no such dialog box, but you can access the two variables associated with "simplify-way" from the preferences, look preferences (`F12`, or `Edit→Preferences`).
* Select the "Advanced Preferences" tab (only visible in Expert Mode).
* Look for "simplify-way." `simplify-way.` among the configured variables.variables.
* You will find both the the numerical value at `simplify-way.max-error` and your boolean setting at `simplify-way.remember`.
* Now decide if you want to change the latter from `yes` to `no`, or if all you wanted was just to be able to edit the numerical value you had entered.