Heater box rubber plug

[Robs931]

Probably a long shot,

I seem to have some sort of plug/blank missing from the RHS of the heater box in my 2019 Citroen Dispatch van. At the moment I have an oval shaped hole under the pollen filter cover, that is just blasting out freezing cold air on to my feet. After watching some YouTube videos and looking at pictures I can see there is supposed to be a plug blanking off the hole (circled in red on the attached picture). Would anyone happen to know the part number of the missing bung at maybe the size of it so I can try to find a replacement?

TIA.

[PaulC5]

Until you get a plug some duct tape might cover the hole.