how to eraise ipad with cracked untouchable screen?

Go to the link below. Scroll down to 'If you no longer have your IOS device." Start at step 2.

What to do before selling or giving away your iPhone, iPad, or iPod touch - Apple Support

Here it is. 🙂

If you no longer have your IOS devce.

If the steps above weren't completed and you no longer have your device, follow these steps:

1. Ask the new owner to erase all content and settings as described above.
2. If you're using iCloud and Find My iPhone on the device, sign in to icloud.com/find, select the device, and click Erase. After the device has been erased, click Remove from Account.
3. If you're unable to follow either of the above steps, change your Apple ID password. This won't remove personal information that's stored on your old device, but it will prevent the new owner from deleting your information from iCloud.
4. If you're switching to a non-Apple phone, deregister iMessage.
5. If you're using Apple Pay, you can remove your credit or debit cards at iCloud.com: Choose Settings to see which devices are using Apple Pay, then click the device. Next to Apple Pay, click Remove.