The star washer is a push fit on the spacer. Push the first washer off the spacer, butt it up against the ridge and push the spacer in from the sprocket side with the other washer on.
Or else, just get rid of the washers. It's just the spacer you need to hold the bearings. I left mine out without any consequences.
Unless anyone knows better, I can't for the hell figure out why they're there at all, except maybe for keeping the spacer centred when pushing the shaft in, although I never had any problem with that. The spacer can't slide out of centre that much. If it does, all it needs is a bit of a wiggle when pushing the shaft in.