Deactivate Viber account on different device
Refer to Viber's official guide on how to Deactivate your Viber account (Mobile):


  
  Open Viber
  Enter the More Options menu
  Select Settings
  Select Privacy 
  Select Deactivate Account
  
  
  Deactivation can only take place within the application. If you have
  uninstalled Viber and would like to deactivate your account, you will
  need to re-install Viber in order to do so.