If you are looking for a way to backup or restore your iPhone Viber chats, have a try on Dr.Fone for iOS. It backups iPhone Viber chats, call history and attachments like audios, videos, documents, etc. to Mac and restore them to iPhone at any time.

youtube.com/watch?v=qR1rE-SLOWg
Workable iOS devices:
iPhone 6S, 6S Plus,
iPhone 6, 6 Plus
iPhone SE, 5S, 5C