You can downgrade Enterprise to Pro using generic key.
-Disconnect your device fro inernet
-Go to Settings / System / Activation and select Change product key
-Enter generic key VK7JG-NPHTM-C97JM-9MPGT-3V66T
-Restart and connect back to internet
That shoud reactivate your device using license you have purchesed online.
Note: Generic key can be use to cheange edition, but it can't be use for activating Windows.