Preferably use a laptop / PC and Chrome that combo seems to work well,  not the app or mobile browser,  then you can manually change your tracking this way:
 
- Go to "Orders Paid & Dispatched"
 
- Click on "View order details"
 
- Within the "Postage" section there's a small dropdown arrow next to "Track Package" - click on that.
 
- Click on the "Add tracking" option
 
- A box will come up with the current tracking number . Delete that and replace it with your tracking.
 
@edbucko0151