Not sure exactly on the Clio but door cards are much of a muchness.
TBH, there is probably a vid on you tube?
Find any screws and remove...generally on door pull, hidden in handle release (small cover to pop out) and maybe at bottom.
Remove release trim...often only the screw holds, may have clips or need to be slid a little.
Work from bottom corner and pop plastic trim holds that hold the card on.....big screwdriver
Lift to clear window trim and check for any electrical connections that may need removing.
Carefully peel plastic liner or neatly cut (reseal with duct tape)

When you can see inside of handle mechanism and bottom of door internals, you can start to work out what's bust and how to fix.... may need a new handle?

 

A cable has probably come off from the door handle to the door actuator.

 

Does anyone know how to get the retaining clip (blue ) off the linkage rod inside the door please? Got the door card removed and this is all that's holding the handle on now but how to unhook it from the linkage rod? Has anyone replaced an external door handle before?

There's a photo of the retaining clip on the new handle as well. I think it's slightly different to the original but similar

 

done with a bit of force...

 

Nothing like a bit of force to solve a problem

Lever over the rectangular pad???

 

Broke the blue retaining clip off the handle, but it still remained attached to the rod but was easier to remove on its own. Door lock button sticking now must have knocked something.

This was the problem anyway, part of a spring had sheared off

 

For anyone else attempting this mark on the linkage rod with a marker pen the position of the retaining clip top and bottom before removing the old handle and make sure the retaining clip of the new handle goes in exactly the same place.

Haynes says something like take careful note of the position before removing- but this translates as take careful note of the position before removing because if you don't then the doors will lock but not unlock! It seems if it's slightly out then although the handle still operates fine to open the door, the separate rod which operates the door lock button won't pop up fully when the central locking is operated and won't unlock the door.