If you used the postage label supplied via ebay you won't need to mark dispatched or add the tracking, it happens automatically. If you bought your own postage and the link is not via the dropdown arrow next to the item on your orders list you can contact ebay and ask them to do it. You can use callback on here: https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid