If you have deleted your default Google Calendar, Google will automatically recreate it as a new, empty calendar (so that your Google account still has a default calendar). You can use Spanning to restore your deleted calendar back into your active Google account, but, that restored calendar will be a newly created "Restored From (date)" calendar.
If you want this restored calendar to become your default Google Calendar again, it will be a manual process to individually re-assign each of the events in the restored calendar back to the default Google calendar.
Alternatively, you can export your backed up calendar data out of Spanning to a .ics file to your local hard drive. You can then import this .ics file directly back into your default Google calendar. If your backed up calendar has many events, this export / import process may save some time in recovering your Google calendar, as you won't need to individually re-assign each calendar event to the appropriate Google calendar.
For additional information on how to download your export data to your local hard drive, please refer to the Knowledge Base article below:
How do I download my exported data?