Use a net tie. For now you need to use a the workaround of a symbol/footprint pairing.
Or depending on your application don’t connect the planes directly but via a ferrite bead.
However: Make sure that you really benefit from separate grounds in your system. Splitting ground planes does not automatically improve the system behaviour. If done wrong then it might achieve the exact opposite. For example if a trace crosses the gab between the two planes then you have created a wonderful slot antenna. (you will need to offer a low impedance ground path in parallel to that trace.)