Forrest Sawyer, the former "CBS Morning News" co-anchor who left CBS last year, will be back on the dawn patrol for ABC News as of July 11, when he succeeds Jed Duvall as co-anchor of "World News This Morning." An ABC spokesman said Monday that Duvall is being reassigned at his own request. Shortly after Sawyer starts work, his ABC News program--now broadcast from Washington--will be moved to a new home in New York. The program's female co-anchor is Paula Zahn, recently named as the official successor to Kathleen Sullivan . . . who now co-anchors the "CBS Morning News."