Complex sentence: He made his first Premier League appearance on 7 May, coming on as a substitute against Arsenal, before starting Manchester United's final match of the season on 21 May, a 2--0 win at home to Crystal Palace.
Split into simpler sentences: He made his first Premier League appearance on 7 May, coming on as a substitute against Arsenal. He started Manchester United's final match of the season, a 2-0 win against Crystal Palace.