Q: forgot icloud account on ipad and its locked

Check these articles and follow the instructions.

If you forgot your Apple ID  - Apple Support

If you forgot your Apple ID password  - Apple Support

https://iforgot.apple.com/appleid

If you have purchased second hand device:

You need to contact the seller and ask him to remove this iPhone from his list of devices. Otherwise, your iPhone will be a useless brick.

Find My iPhone Activation Lock: Removing a device from a previous owner’s account - Apple Support