Replaced engine.

Hi all, last year my C70 2.0 engine had died, bad idea running without oil... anyways the garage thought it might of been the big end bearing or small not sure but had that replaced but they said it could of been something else and the only way to find out was to replace this bearing which I did but it went straight away.. so purchased another C70 T5 and had the other ones engine replaced, I'm now selling the 2.0 with this new engine but a few people have told me to register the engine with the dvla..

how i.e. do I go about this? I know it's probably straight forward