how to remove 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, or unless you can secure the cooperation of the previous owner, you’ll not be able to defeat or bypass the Activation Lock. Without documentary evidence that you are the original owner (such as sales receipt showing the serial number), Apple won’t assist - and nobody here will be able to help you.

If you are the owner of the AppleID that previously activated the device - and 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 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

After you have recovered access to your AppleID account, given that you’ve changed your email address (that identifies your AppleID account), you’ll need to update your AppleID to reflect your primary email address. Here are the processes to make this change - and, critically, the steps that you need to follow having made changes to your AppleID account:

Change your Apple ID - Apple Support

Change your Apple ID password – Apple Support

What to do after you change your Apple ID or password - Apple Support

Hopefully this information helpfully resolves access to both your AppleID account and your iPad.

Turn off Activation Lock - Apple Support

You should be able to turn it off even if you don't have access to the original email address anymore - as long as you enter the email address and password used to setup the device.