You have only two option.
1. Bring back all tapes in library and perform the Phase I. It will show all images in java console catalog > import tab.
Generally, the customer use the opscenter to maintain the report which storage have what data. (Recommended option)
2. Bring back all tapes and perform robot inventory and run the media content report against the media. (This time consuming process)
In both condition you have to bring back all tapes to library.
It is highly recommended to try to understand the general order in which the tapes were written to. For example, create a list with the first tapes that received data at the beginning and the last tapes that were written to at the end.
The reason for this is that when you start Import Phase I, the reindexed metadata will be expired after a week and there's no way you'll import everything in only one week. This means that if a backup spans two tapes, then the option to Import Phase II for that backup will not show up unless both tapes have their metadata reindexed at the same time.
If you don't have a list, what will happen is that you'll only be able to import the backups that are only contained on single tapes. When you finish, you'll probably need a second run for all the backups that span over multiple tapes, but by then the imported tapes will show you their original assigned date which will allow you to import again the tapes, now in the proper order.