In case, the tracking numbers are updated incorrectly by FulfillSync. There is a way to correct the tracking number. Please follow the steps below: 

1. Ensure the source is switch to File Upload and mapping are corrected.

2. Click on Start Upload

3. Enable the option Update fulfilled orders too

4. Upload the correct shipping file and wait for the process to complete.

Note: Updating fulfilled orders does not handle partial fulfillment and this option will make the process slower.