As the iPad is brand new, it will have iPadOS15/16 installed out of the box. As such, this support page to be helpful:
If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support
There is no requirement to connect an iPad (or iPhone) to a computer during initial setup - and in reality, many such devices are never connected to a computer. As described, even if setup wasn’t completed, your “customer” may well have entered a Passcode - and in likelihood, this has now been forgotten.
A forgotten or unknown iPhone/iPad passcode cannot be recovered - and neither can it be reset or modified from another device.
iOS/iPadOS 15.2 or later with a forgotten Passcode
Apple has introduced a new procedure with which to reset an iPad or iPhone with a forgotten Passcode - allowing you to use your AppleID and associated Password to reset your device.
How to reset your iPhone, iPad, or iPod touch when you forgot your passcode - Apple Support
You will be able to restore data from a pre-existing iCloud backup without the use of a computer, but will require a PC/Mac to restore data from an iTunes backup.
iPadOS 15.1 and earlier - and all devices that are Disabled
If your iPhone/iPad indicates that it is disabled/unavailable/locked-out, or you have forgotten your iPad passcode, you have no alternative other than to follow this process:
If you’ve forgotten the passcode on your iPad, or your iPad is disabled – Apple Support
You’ll need access to either a Windows PC (with iTunes for Windows installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of macOS).
Download and use iTunes for Windows – Apple Support
Update to the latest version of iTunes – Apple Support
Use of a PC or Mac is unavoidable. If you don’t have access to a suitable computer of your own, that of a helpful friend or family member will suffice. Alternatively, the technicians at the Genius Bar of your local Apple Store will be delighted to assist:
Genius Bar Reservation and Apple Support Options - Apple
AppleID
You may also need your AppleID and associated password. If these have also been forgotten, they can be recovered here:
https://iforgot.apple.com
To recover your credentials, you’ll need access to one of the following:
- Your primary email address mailbox that corresponds with your AppleID
- Any of the secondary/recovery email addresses that should be configured for your AppleID account
- Any of the trusted telephone numbers (fixed line or Cellular/Mobile) that are associated with your AppleID
More information about recovery of your AppleID and associated Password:
If you forgot your Apple ID - Apple Support
If you forgot your Apple ID password - Apple Support
