So I recently had some issues with the alternator not sending charge.
I have bought a brand new OEX replacement. All went well with the change over.
When I go to start it, the car starts fine although she won't stay on. Turns itself off once the idles drop.
I can keep it going although I need to keep the revs up.

A few extra notes.
Battery has been disconnected for approx. 3 weeks now.
The battery is now fully charged.
Voltage increases to 14> Volts when car is running (With revs up). So nothing wrong with the alternator.
Car is Nissan Patrol GU 4.8L 2002.

I have been told that the ECU may have been reset since leaving it disconnected for some time. Driving it around will re-configure itself out.

Anyone know or have any insight about this problem?
Can I just drive it around and it will sort itself out?
Can I manually reset the ECU?
Is there another way to fix this without driving it around?