How do I restore a Group address in Tbird Addressbook that I inadvertently deleted, including all the individuals?

I was updating my Address Book in Thunderbird with a new contact that was a member of a Group contact. When I was finished, I noticed that the Group came was listed twice in my Personal Contacts Address Book. I deleted one of the two that were listed, but when I went to send a message to that Group Contact, it was no longer listed. Can someone advise me of a way to restore that Group Contact without having to re-type the entire list--it was a rather lengthy list. Thanks in advance, I hope.