The QR code is a convenient way to access a UID number/ serial number and usually the HTTP URL (web address) of a P2P/cloud server. When those are known it can sometimes be manually typed into an app; the QR code is quick and prevents typos.
If you're missing either of those you're likely out of luck as far as a smartphone app for remote access.
I could be wrong but I'm thinking you'll only be able to access it locally over LAN and even that's assuming you can find its IP address and it has an accessible, non-encrypted RTSP stream.