Use Clear Groovy Caches to manually clear caches if automated clearing fails. Automation should reload classes whenever a script is modified; however, dependent classes can fail to reload.
There are no fields for this built-in script. You just have to select Run or Preview. After you run this script, expect a delay in screen refresh because classes are recompiled when clearing caches.
If you have a custom class file (ClassA) in your script roots and another Groovy script imports that file, modifications to ClassA may not show up until you modify the script that imports them or clear the Groovy cache with this script.