The first step in updating your custom label field in eBay is to download an eBay file of your active listings. Please navigate to your eBay account -> click ‘My eBay’ -> scroll down and you will see a ‘Seller Tools’ section on the left hand side of your screen -> Click ‘File Management Center’
Once there, to download this file, Click ' Create Download Request' on the right hand side of your screen under the section ‘Downloads’
Once you have the file from eBay, please copy the correct SKU into the eBay custom label column on your eBay file.
The last step is to upload the eBay file back into the eBay exchange site by clicking ‘upload file'. This will set your new SKU# as the custom label in eBay!