There are 2 fields in the CSV to specify starting page and length - page and pages. So in your case,
Song1;1;1
Song2;1;2
Song3;2;1
But since the songs are already created, just edit each to have the correct starting page and number of pages.
Song1;1;1
Song2;1;2
Song3;2;1
But since the songs are already created, just edit each to have the correct starting page and number of pages.