The entry note decides the first step
If the chorus starts sharp or flat, the rest is hard to rescue. Train the entry note into a stable response first.
The breath before the high note matters
Many chorus high notes fail because the previous phrase has already disturbed breath and throat coordination. Practice the setup, not just the note.
Increase volume in stages
Sing it softly in tune first, then add volume. Check pitch and clarity at each level so the high note is not shouted.