You should still be able to add via the seller hub, there are two points you can do it if the item is in your paid and dispatched folder Click the circle with the three dots next to the item add tracking should be the 2nd or 3rd option. Also there should be a little +add tracking to the right of the picture of the order.
If on the app I think if you click orders find the item click on it again and just scroll down there should still be a add tracking option.
