In the library, make your listing selections and click the Bulk Actions button.
The Bulk Actions button will appear towards the top right of your screen once at least one listing is selected.
Choose Edit Listings, then Item Specifics.
On the next page you're able to update item specifics per listing or for all listings at once.
The item specific values change depending upon eBay category selected for the listings. Item specifics that are required by eBay are noted with a red asterisk.
To change all at once, for example, enter Brand in the Name field and enter the Brand value in the Value field, then click Update all. If the brand is required on some listings, it will be filled in with the specified value, if brand is not required, a custom item specific will be created for those listings using the brand value. Then select save all modified.
To change the item specifics per listing, enter the values for each required item specific, you may choose from those that eBay provides or enter your own.
To add your own item specifics, select Add a custom detail, enter a custom detail label and a custom detail value.
Once you've completed the changes, select Save all modified.