To copy an address from your eBay dashboard you want to make sure that you are on the orders list page.

Once there you will see the copy button. Simply click that button and the address will be copied into the extension and the button will change to say copied until you refresh your page. 

Note: If you do not see an address under the actions field like shown in the image, then the copy button will not work. Please contact support and inform them of the issue.