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.