In my opinion easiest is to get an ecu kit and replace ecu, driver door key, tailgate, fuel cap and steering wheel one.
Example: https://www.ebay.co.uk/itm/Land-Rover-Freelander-1-TD4-Pre-Facelift-Complete-ECU-Kit-Lock-Set/183929038603?hash=item2ad306670b:g:IYUAAOSwwRtdYYID