There is draft of cold air coming into the house from my conservatory door.

I have noticed that there is a small plastic part that is broken and has left a hole at the bottom of the door.
I don't know what this part is called.
Could someone tell me what it is called so that I can search for and buy it?

[![hole under the conservatory door][1]][1]


  [1]: https://i.sstatic.net/sPkXq.jpg