It’s a pretty simple task to fix it – take off all the loose paint, then skim over with fine finishing plaster (don’t worry about getting it perfect) then, once fully dry, lightly sand so the edges where the plaster meets the old paint are smooth and you can’t feel any ridge when you run a finger over it (fine finishing plaster is a doddle to sand back). I have done similar a few times and it is really easy to get an almost invisible repair.
