If you dismiss the opening Realm Studio dialog (the one that has the open a local Realm and Connect to a Realm Object Server buttons) there is no way to either re-open this dialog or use a keyboard commend equivalent (like CMD-K in the macOS Realm Browser) to open a ROS connection dialog. There should be a Window menu entry and keyboard equiv to re-open this dialog.

(There is an Open... command available from the file menu, but this would seem to be only for local Realms.)

This is as of 0.0.1-alpha.9 (0.0.1-alpha.9.49)