Hello Viberproblems,
Welcome to the Apple Support Communities. From what I understand you're having trouble finding the settings to create a backup of your Viber information. I'll gladly point you to the right place.
Take a look at this information from Viber regarding the steps you need to take to create a back up using iCloud:
1. Open Viber
2. Select the more options screen
3. Select Settings
4. Choose Account
5. Select Viber Backup
6. Choose Back up now
7. Wait while Viber backs up your data to the iCloud (this can take a while)
Please note: you must be connected to your iCloud before you can back up your messages. If you aren't connected to the iCloud service:
1. Open your iPhone settings
2. Choose iCloud and sign in
3. Select iCloud Drive and enable it
4. Scroll through the apps and make sure Viber is switched to ON

Automatic back up on an iPhone
You can set your iPhone to automatically back up your messages. Back up will only happen when your phone is connected to Wi-Fi.
1. Open the more screen
2. Tap on Settings
3. Choose Account
4. Select Viber Backup
5. Tap Auto Backup
6. Choose weekly or monthly"
Viber - Back up and restore Viber messages
If that's still not working, the best thing to do from here is to continue partnering with Viber support for further assistance: Viber | Open a Ticket
Have a great day.