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 issue, entering database and reindexing Jira instance etc. but most importantly but most importantly without change issue Updated field.
Go to Administration -> Manage apps and select Bulk Fix Resolutions.
Under field Change resolution in 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 are changed to the specified new resolution.