How do I replace the headlamp washer mechanism that extends to spray fluid?

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I need to replace the driver's side headlamp washer cover on a 2005 Volvo XC90. In checking the sprayer mechanism that the cover mounts to, I find that the plastic mounts on the mechanism are broken, so i ordered a new mechanism. It has an O-ring seal around the tube end. How do I change out the old mechanism for the new one? Thanks for any help!!