Fitting externally sprung forks can be a real hassle unless you know the wrinkles. Remove the lower yoke pinch bolt, carefully tap in a flat bladed screwdriver just enough to expand the fitting allowing the stanchion to pass through. A drawbar can be used to pull/refit the stanchion back into the base of the top yoke. Your bike will probably run an axle with the correct screw pitch but if not get a rod threaded and add a crosspiece. Screw the rod into the top of the leg, pull up until it registers into the top yoke, maintain the tension, remove the screwdriver, fit the bolt and remove the drawbar. Fit the top bolt through the yoke and check everything’s properly in place.