What is this conservatory door part called?
This is one of those questions without an answer--the part is a proprietary component of the door's astragal, the dividing bar between slabs that provides a latching face and weather seals. You can contact the manufacturer or supplier, or you can attempt a repair.
I'd look at using pop rivets or sheet metal screws along with caulk and some plastic or aluminum sheet to overlay a plate that matches the original size and shape of that part. Add weather stripping if needed to help seal any remaining gap.
Show more photos from different angles for more specific suggestions.