Original: However, he also returned to his chair in the cello section, and participated as cellist in the world premiere of Verdi's Otello (La Scala, Milan, 1887) under the composer's supervision.
Simplified: When he got back to Italy Toscanini returned to his chair in the cello section, and took part as cellist in the first performance of Verdi's Otello (La Scala, 1887).