This should normally be finished by a contractor who understands how the window comes aside. The sash (the body that holds the panes) is removed and it is then disassembled as a way to take the IGU out. A new replacement IGU (ordered with the window manufacturer) is then fitted https://eyebrow-shaping-tools21098.blogdon.net/secondary-glazing-can-be-fun-for-anyone-50647700