Advice needed

[Greg_0ry1]

Got a bit of a shock today during some diy work in our bedroom, please take a look at the images and maybe someone could suggest the best way forward. It looked like the old wallpaper kept all together for some time so need to fix that rather soon.

 

[Greg_0ry1]

Anyone who could give some advice how to approach this? My initial idea is to insulate with a thin layer and plaster the rest but I am unsure if this is the right approach so would be thankful for some advice.

Thanks