Can't Log Out Old Viber Account on our iMac

We have an iMac at our office that has a former employee's Viber account logged in. I tried uninstalling it, but every time I do, their account stays logged in, asking me to scan QR code. Scanning the QR code doesn't work when I use my device and there is no way to contact this former employee now. Is there any way I can log out their viber account? Thanks