I used to use Viber on iPhone for a while with one set of Viber credentials.
Now I want to reinstall Viber on the same device "erasing its memory" completely: to use it with completely different identity (phone number, name, chat history) -- in a manner that Viber has no way of knowing that it was previously used with a different number on this device / for this Apple ID etc.
iOS 12.x throughout my Viber usage; currently 12.1.2.
Update (2019-02-07): Here what I tried so far, with no success:
Settings > General > iPhone Storage > Viber > Delete App(per 1)
Privacy > Advertising > Limit Ad Tracking; followed by
> Reset Advertising Identifier
AppleID > iCloud > Viber > Off
- disabling backups for Viber (per 2)
AppleID > iCloud > Manage Storage > Backups > (my phone) > Delete Backup
- rebooting between the above cleanup steps and installing a new copy of Viber
- completely signing out of AppleID, which includes removing all AppleID account-connected data including Keychain and disabling access to any backups
- starting a newly installed Viber when the phone is in Airplane mode (per 3)