Unfortunately, this cannot be cleaned. The glass must be replaced. Insulated Glass (IG) windows are a sealed unit of two panes of glass with an inert gas in the space between them. When the seal is broken and the inert gas leaks out, you eventually get condensation between the panes, which leads to haze, fogging and eventually ‘funk’ growing between the panes. Maybe you’ve seen a green window someplace. There is no practical way to clean and reseal these fogged IG units, they must be replaced.
Note that replacing the insulated glass panels in your windows can be done without replacing the window itself. Most glass companies can service the window, including the balance rods (which keep them open) and locking hardware when they replace the glass panels.