A forgotten or unknown iPhone/iPad passcode cannot be recovered - and neither can it be reset or modified from another device. Any attempt to reset the iPad will likely trigger an Activation Lock.
Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be satisfied:
Activation Lock for iPhone, iPad, and iPod touch - Apple Support
Turn off Activation Lock – Apple Support
As you will discover, unless you are the owner of the AppleID that was last used to activate the device, you’ll not be able to defeat or bypass the Activation Lock. With documentary evidence that you are the original owner (such as sales receipt showing the serial number), Apple may be prepared to assist - otherwise they and nobody here will be able to help you.
If you have the necessary documentation, Apple have introduced a portal though which you may be able to request release of an Activation Lock:
How to remove Activation Lock - Apple Support & start an Activation Lock support request.
However, this isn’t necessarily the end of the story...
A close Family member or Executor, with the required supporting paperwork, can make application to Apple to be granted access to the Apple accounts of the deceased:
How to request access to a deceased family member's Apple accounts - Apple Support
You should note that if successful, this process will grant access to some information stored in iCloud - but will not, of itself, resolve access to the iPad.
Quite often, close family have sufficient knowledge - and access to likely recovery paths - that access to the AppleID account of the deceased family member can be recovered. Having done so, it is then possible to release the Activation Lock that prevents reuse of an iPad/iPhone.
The following guidance is written from the perspective of the owner - but a family member will get the idea as they run through the process.
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If your device is Activation Locked, this help page will provide most of the information that you’ll need:
Activation Lock for iPhone, iPad, and iPod touch - Apple Support
If you have forgotten your AppleID or associated password, these can be recovered here:
https://iforgot.apple.com/
To recover your credentials, you’ll need access to any 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
Having recovered access to the AppleID account (and therefore the AppleID username and associated Password), Activation Locks can be removed. There are several routes to this, but for brevity, I’ll refer you to this support page:
Turn off Activation Lock – Apple Support
If your intent is to wipe/reset the device(s) for reuse by a new user, you would be best advised to prepare them properly:
What to do before you sell, give away or trade in your iPhone, iPad or iPod touch – Apple Support
