Airplay can be configured to use a password to allow only authorised people on a network to use it.
As PeakMan suggests you may have originally created one during setup.
I don’t have a Qb, but the password is set on the output device and would not be an iPad setting itself - though if setup of the Qb is done via the Naim app I’d imagine there’s be an option during that process.
I can’t see an option in the App currently to change it, though it may be somewhere I don’t expect it.
There are web interfaces to access some of the devices, for example on my Nova:
On a Mac these used to be accessible in Safari via the Bonjour services tab, but Apple got rid of that display preference - can’t remember if there was an option on iPad Safari.
There’s also a different webclient to control various things someone mentioned recently.
As these web interfaces are perhaps not officially described probably best to avoid them if there’s a simple solution (including a factory reset and setting up again).
I hope it’s not a compatibility issue between Airplay 1 functionality (which your iPad may have) and Airplay 2 which is in current Naim firmware.