Replacing bathroom fan vents into attic
In this case what I would do is first remove the soffit panels between the roof trusses where the fan is. Take some rigid wire and fish it above the insulation to the fan hole. Tape the 4 inch flex duct to the wire and pull it to the eave from the outside. Then attach to the fan and eave louver. Replace soffit and anchor the louver in places with screws to the soffit panel.