Resolutions are a great way to track issues in Jira and check what has been done and what still needs to be done. But from time to time resolutions might be set even though the issues aren't finished, yet.
With the following rule the resolution will be removed from all issues that are not in status category "Done".
Add a Trigger → Manual
No further configuration needed. The rule will only be executed if a user hits the Execute button.
Add Selector → JQL Selector
Use the following Expression:
Update field action
Next to the JQL Selector click on Add → Action → Update field
Choose No value - clear field
This is how the configuration above should look like on your screen