Thanks for posting your question here. Since you have already opted into this program (called the Global Shipping Program) through your eBay account, all you should need to do to make the option available when listing through Auctiva is generate a new token from within your Auctiva account.
You can generate an eBay token by mousing over the "My Account" tab within your account, selecting the "eBay" option under "Settings", clicking the "Get New Token" link on the ensuing page and then proceeding as directed.
Once you have done so, you should see a new option called “Global Shipping Program” in the Shipping Tools section when listing your items through Auctiva which you can select to utilize this option in your listings.
If you do not see this option within your account after generating a new token, please contact our Customer Support team from under the “Help” tab within your account and we will be happy to continue working with you on this.