How do you restring a two string weed trimmer

If its what I'm thinking here you simply push the string to wards the center of the hub and the new line comes in from the outside through that hole and the cams there grips it automatically. Sometimes the old is hard to push in to get it out and you need a small screwdriver to push it through the hole.

So if there's a cap on the center of the string area under there is where the strings gets pushed through.