Bulk Fix Resolutions
Available since 1.47.*
Use the Bulk Fix Resolutions to change the Resolution field on multiple issues at once. This functionality allows you to modify the Resolution value for all issues returned by a saved Filter or JQL query without transition the issue, accessing the database and reindexing Jira instance etc., but most importantly, without changing the issue Updated field.
Go to Administration -> Manage apps and select Bulk Fix Resolutions.
Tip: Use a Keyboard shortcut: g + g + then start typing Bulk Fix Resolutions
Under the Change resolution in field you can choose whether you want to make changes in the Filter or in the JQL query.
In New Resolution, select the correct resolution value. For Unresolved, select None.
Optionally, click Preview to see an overview of the changes before running the script.
Click Change - all issues matching the saved filter or JQL will be upated to the specified new resolution.