You can remove/delete Master Bills that are pending discovery by OpenTrack. Here is an example of what this might look like:

Once you click on the remove icon, you'll be prompted to confirm "Stop Tracking" which will remove the Master Bill + associated containers from your account:

For Master Bills + containers that have already been found by OpenTrack, you won't have the ability to delete them since OpenTrack has already provided tracking for them and will count towards your monthly usage.