It's fairly easy to achieve that. Follow the instructions on either of this pages:
You simply need to apply proper filter (the one from you question). Click on Tools (upper right corner). Check the checkbox in front of each ticket you want to update (or select all) => Edit Issues option and from there select Change Priority with the proper value you would like to set and confirm.
If you spend enough time as a Jira admin - whether you are managing a single, mid-sized instance, a large enterprise one or juggling multiple instances at once - you will eventually find yourself in ...
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