I think I transferred stuff from my iPhone instead of old iPad how can I fix?

Reset the new iPad back to Factory Settings including erasing all data from the iPhone. Once that resetting has been completed, then can restart the process and use the correct device to transfer data to the new iPad.

To reset to factory settings, on your iPad, open Settings ➔ General ➔ Transfer or Reset iPad ➔ Erase All Content & Settings.

Axel F.