NOTE: This suggestion is for JIRA Cloud. Using JIRA Server? See the corresponding suggestion.

Hi everyone,

Thanks for voting and commenting on this issue. Your input in the comments helps us understand how this affects you and what you're hoping to accomplish with JIRA.

At this time, this suggestion is not on the JIRA development roadmap. We suggest the workaround described below.

Please remember that jira.atlassian.com is one of many inputs for the JIRA roadmap. You can learn more about our process here.

I understand that our decision may be disappointing. Please don't hesitate to contact me if you have any questions.

Regards,
Dave Meyer
dmeyer@atlassian.com
Product Manager, JIRA Platform

Please try the workaround listed here: HowTo: Bulk Edit Resolution

or
Use a CSV export / import

1. From Filters > View all issues, search for the issues you want to update
2. Ensure you include the columns you need to be exported. The columns you must include are Key, Summary, Resolution, Resolved. 
3. Next, click on the Export > Export Excel CSV (my defaults) button at the top right corner. This will trigger a download of a CSV file to your computer
4. In Excel, edit the CSV file (make sure you keep the date format), updating the Resolution field to the desired value and export or save it in UTF-8 encoding – Note: For Resolution field, make sure you select a valid value listed on your Resolution settings page (https://<your site name>.atlassian.net/secure/admin/ViewResolutions.jspa).
5. To import the CSV, go to Jira settings > System > External System Import (https://<your site name>.atlassian.net/secure/admin/ExternalImport1.jspa) and follow the prompts
6. On the Map fields page, ensure you map Issue Key to Issue Key, Summary to Summary, Resolution to Resolution, and Resolved to Date Resolved.
7. Continue with the prompts to complete the import.