How correct error of inserting only one quarter note when I need room in a 3 eighth notes kick off?.

Its a 12/8 piece with a kick off measure that has only 3 eighth notes. How can I go back to the beginning to correct this? Do I just have to start all over? If I must start over how do I delete the screwed up first score try? I can't delete or otherwise make a Score go away. I don't want to accumlate a horror museum collection of every score I messed up so bad I had to start from the beginning a dozen times.