How do I shift notes so that they do not overlap?

You can move each element in FORTE using the keyboard. This is possible with notes as well, in order to adjust spacing between notes.
First switch to selection mode 'CTRL + 1' and then click on the note you want to move. The note will now be displayed in red. Press and hold the CTRL key and move the note using the arrow keys (left and right).
This way, you can also correct the pitch. Use the arrow keys (up and down) as well.