How can I reset my password on an old IPAD mini (from 2014) when there's an Activation Lock?

Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be turned off:

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.

You’ll not find commercial software that can remove an Activation Lock - as the lock is implemented in Apple’s back-end activation servers. There is nothing that can be done to the iPad that can remove the Activation Lock; it is the Activation Server authorises use of the iPad when the correct credentials are entered.

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.

Presumably you are now using a different AppleID account to that used to activate your old iPad. Recovery of the previous AppleID credentials, should be possible…

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

Unless you AppleID account has not been fully/correctly configured, or has been seriously neglected, recovery of the AppleID and password should not be difficult.

More information about recovery of your AppleID:

If you forgot your Apple ID - Apple Support

More information about recovery of your AppleID password:

If you forgot your Apple ID password - Apple Support

When you recover access to your credentials, you would be well advised to log-in to your AppleID account from a web browser - and verify/update any email addresses and trusted telephone numbers:

https://appleid.apple.com/

Hi ThxinAdvance111,

Welcome to the Apple Community.

Apple Support's article:

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Says

" Your Apple ID password or device passcode is required

before anyone can turn off Find My, erase your device, or reactivate and use your device". 

Wondering if you know the Apple ID password ?

Eg: You may be still using that with your iPad mini ?

You might want to scroll down the (above linked) article to:

"If you forget your Apple ID or password" to view the details :

All the best :-)