how to unlock ipad with icloud?

Do you mean this? -->

Mar 2018 - Possible (unverified) tip on recovering from a disabled state if you have no access to a computer but do have access to another mobile device and a recent backup - https://discussions.apple.com/message/33099578#message33099578 - Use the Find My app or a computer web browser https://www.icloud.com/find login to erase the disabled device and then restore the device from its backup. More at iCloud: Erase your device with Find My iPhone - https://support.apple.com/guide/icloud/erase-your-device-mmfc0ef36f/icloud

If you mean Activation lock:

Activation Lock for iPhone, iPad, and iPod touch - Apple Support - This is a security feature, in part to deter re-selling of stolen devices. To learn more click here --> http://support.apple.com/HT201365

Turn off Activation Lock. To read more click here --> https://support.apple.com/HT201441 - An activation lock can only be removed using the log-in information for the account that applied the lock.

If this is a device for which you are not the original owner, get the owner of the account to remove the lock or return the device for a refund. The device is otherwise useless to you. If the owner has not provided contact information as a message showing in the login screen there is no way to contact the owner unless the person who gave you the device knows them.

If you are the original owner and have forgotten the log-in information, try to recover it:

- "If you forgot your Apple ID" [this is likely an email address you are using or used in the past] click here --> https://support.apple.com/HT201354

- "If you forgot your Apple ID password" click here --> https://support.apple.com/HT201487

Otherwise:

Apple may possibly remove a lock if a person can provide sufficient evidence of valid ownership. The device is normally taken to an Apple Store with identification and the original sales receipt. I.e., the receipt when the item was sold to the first owner, and preferably by that person. This is unofficial and there is apparently no set policy (I asked at an Apple Store). A store may simply refuse, particularly if they are not satisfied you have proven ownership by provenance.