I can’t seem to track down the “Immobilization Setup” procedure anywhere. Can someone please fill me in or direct me where I can find this info?

Due to various issues, I’m trying to replace my 1999 XK8’s ECU. The only info I’ve been able to track down has to do with reflashing the ECU with a “Mongoose” device and certain PC software? Is that the same as the immobilization setup?