I do not know if this the right forum. Is there a way to change mail forward in the round cube client by the user.T he only way I find is out of of ispconfig.
If the ISPConfig RoundCube plugin does not has such a function, then you can only change it in ISPConfig. Email users can also log in to ISPConfig using their email address and email password.
The plugin has that option, among other options. Different options can be enabled individually. https://github.com/w2c/ispconfig3_roundcube