Use the Inventory Details page to batch update properites of existing inventory, including:
Use the Inventory Filters on the top of the page to refine the results.
Select the item(s) to edit using the checkboxes on the left side of the table, then click the "Checked Options" button on the top right of the page to open more options and "Edit Selected."
Choose the property and the value the property should change to. Click the "Apply" button to initiate the change.