Unfortunately the Fretboard Editor can not rotate a fretboard diagram so that it lies horizontally.

As a workaround you can create a horizontal fretboard in the Shape Designer.

In the attached Finale document I have created a shape expression with a “generic” fretboard diagram.

You can create custom fretboard diagrams by duplicating the existing diagram, and edit the duplicates:

Delete the circles you do not need, fill some circles with Black.

Also, consider setting up a new expression category solely for the horizontal fretboard diagrams.

Have fun.

http://www.finaleforum.com/download/file.php?id=3616 

@ Peter Thomsen

Thanks for your answer.

It seems more complicated than I thought.

But I'm going to try, Thank you!

Quoting power user Zuill:

“In a similar way, if one likes the Seville font fretboards, one can create expressions that use them as Arrowheads, with a zero thickness line.

Zuill”