Buying New Car and Part-Exchanging my old RHD car

My RHD car has been registered in France for 7 years. I am part-exchanging it for a new LHD car from Dacia at a local garage. What do I need to do (if anything) to “de-register” myself from my old car ?

In UK you used to send off the bottom tear off bit of the registration document to DVLA; but I cant spot anything similar on the carte grise.