The Insert button.
If the Insert button on the Status Bar is activated, the notes are inserted rather than added. That is, any existing notes are moved to a later position to make room for the new notes.
With Insert on, and the Step Position here...
...the new note is inserted, and the following notes are “pushed forward”.
You can activate playback at any time and from any position, to hear what you have done. Please note, though, that moving the Song Position also moves the Step Position.
Click on the “MIDI connector”, and the Step button is automatically deactivated.