sing the same tune

can't carry a tune in a bucket

Sings very badly.

change one's tune

To reconsider; rethink; to reach a different conclusion.

sing a different tune

To hold a different opinion or appreciation (about something); to possess a new, changed, or regenerated mindset, usually for the better.

sing along

To sing some music while someone else is singing or playing the same piece of music or while it is being broadcast or performed

sing for one's supper

To work in exchange for some reward or recompense.

sing from the same hymnbook

To make the same or similar statements, especially to express the same opinions in public as a result of a prior agreement.

sing off the same hymn sheet

Alternative form of sing from the same hymnbook.

sing small

To assume a humble tone.