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Down the left hand side of the screen, there are checkboxes.
Tick the checkboxes that you would like to bulk re-open.
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After selecting the records are ticked, scroll down to the bottom of the screen and click on the Bulk Actions Dropdown
Choose the 'Re-Open' button
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This will take you to a Bulk Re-open page asking you to confirm the open.
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After checking, you can click on the 'Re-Open Matters' button to open multiple matters.