For making it easier, you can check my steps:
You can go to our Ali Orders Apps Dashboard > Import List > Images
Then you can drag the image which you want it to be shown first > Drag it into the biggest spot for your image.
After these steps, you can simply click on the button "Push to Shop" It will be shown with the product avatar which you have dragged in Import List.
Make sure this only worked for product which hasn't pushed to shop.
I hope this might be helpful for you.
Please drop us any message if you have any concern about those steps above.