It is better if you tell me the full sequence of steps you take, not just the one where the failure occurs.
This is what I do:
Open Memento, touch the three vertical dots at the top left, touch "add library", touch "Restore from Google Drive"
A list of libraries should then appear. If this does not happen, it would suggest that you have no synced libraries on that account.
All is not lost. You can recreate the library manually.
Look at your CSV file using a text editor.
The first line contains the names of the fields. You need to create a library with fields whose names exactly match the names in that first line.
Save the library.
Open the library and touch the three dot menu, -> "Import and export" -> "Import from CSV"
If you have done everything correctly Memento should import the data from the CSV into your library.
Repeat for each library in turn.