Tap Credentials and enter your ID and password for VNC access to that computer.
Setting Up VNC on Your Computer
It takes two to VNC. You need to set up your Mac or
Windows computer to accept the connection and allow your iPad to take
over the screen. On a Mac, you can do this by turning on Screen Sharing
in the Sharing pane of System Preferences. On Windows, it is called
Remote Desktop, or you can install a third-party VNC server.