I've recently had wallpaper stripped and the guy managed to remove two of the PVC window trims in the process. This has exposed a gap between the top of the window and the wall of about 1.5 inches, and the same at the bottom beneath the sill a gap of approx 1 inch on half the length of the sill (see pics). The holes go right back about 5 inches deep. I haven't removed the other two sides of the trim but I can see behind them and the main gap is at the top and bottom of the windows.
I don't like the trim any way so happy to remove all of it, but my question is... how do I fill these gaps before I get the plasterer in? Do I need a tradesman to do this properly or can I do this myself - I am a complete novice with limited DIY experience albeit I am willing to give it a go if simple!
I've read that expanding foam might work, is the right? The room will be skimmed after I get this fixed, will I need to replace the trim afterwards or can I just caulk around the edge of the window to the new skimmed plaster? Any help greatly appreciated on how to fix this.