Eagle: Connect polygons / ground planes
You should be able to create vias in the polygons, name them to match the names of the polygons, and then connect with a trace. If a conductor (via or trace) does not have the same name as the fill (polygon here), then Eagle will add space to prevent the signals from shorting together, as happened with the CSN via towards the side of your picture.

You could do this with just appropriately named traces too, but I don't see how you can do it without vias in this image.

As this answer implies, both polygons need to have the same name to be connected.

To do this without adding the via, you can add an arbitrary trace by going into Route mode and ctl-clicking inside the polygon. That method can be a bit wonky, so it might be easier to add the vias, make the trace, then remove the vias.