Paint peeling off due to leak. How to rectify..

[eod]

I need to paint a wall at the local nursery where there has been a leak resulting in the paint peeling away from the wall over a rather large area.

I’m not sure exactly what the wall is made of. It isn’t plasterboard but more like a strong cardboard panel! At least that is what it feels / looks like in the area where the paint has peeled off.

What is my best bet? Would i ever be able to paint over even the whole wall inc. the stripped part successfully?
Or do i have to carve into these wall panels & replace them. And then would that require a skim coat prior to re-painting if i replaced them with new plasterboard?

thanks in advance for any tips

[gc1967]

Stain block the area and skim with easifill and rub down and then paint the wall