Select the ‘cutting-box’ and use Edit>Cut.
Now Edit the side-wall component and then edit the central component part of it that will want the hole.
You’ll know when you have gone deep enough in the edits as you’ll be able to select just one face in that context.
Now use Edit>Paste-In-Place to add the ‘cutting-box’ back inside this context.
Now treble click on a plank face in the context - so that all of the geometry forming the central part is selected.
Context-menu > Intersect > with Context.
Delete the ‘cutting-box’.
You should now see the cut outline in the geometry of the central part.
Use a fence to select just that which you want to be gone… and delete it.
You now have a hole through the central part.
Exit the edits back to the Model context.
In the SKP you posted both side walls are copies of the same component.
If you want the hole to be punched in both of them, then doing the above steps on one also changes the other.
But if you want the changes to apply to just one you need to use the Context-menu > Make-Unique on the selected component-instance, before changing it, so that then those edits only apply to that one,
