If you would need to remove the subtitles of single items listed on eBay, you can scroll down to the eBay section once you open the item in the product editor and click on the Show subtitle button. Once the field is displayed, you can clear the previous values and put DELETE instead and when you either relist or update the item without skipping the particular eBay instance the item is listed on, then the listing would be successfully updated and the subtitles would be removed. Please bear in mind that the value in the subititle field/header is case sensitive and it has to be in the exact same DELETE format and please see the example screenshots below:

If you would need to remove the subtitles of multiple items/listings, you can do that easily in bulk and if you put DELETE in the corresponding ebaysubtitle header and submit the bulk edit file for processing without skipping eBay, the requests would be pushed to the channel and plese see an example below:

NB! You can also download a spreadsheet with the most common bulk headers and valid values and please see the attached file.