I have just changed the engine and gearbox, do I need to rest the ECU?

What is your question?

I fell like my car is running rich at the current time, I don't know if this is just as the new engine adjusting or something or if I might need to rest the ECU. I'm hoping that it might not be something like a leak. Thanks for looking. I might have more question as I'm a new car owner and it seems I have a bit of a lemon.