change tune

To change one's attitude, opinion, manner, or stance on something, typically in a way that is more positive or agreeable. The mention of a hefty tip really changed the host's tune, so I think he'll be able to find us a table after all. After I threatened him with no allowance, my son changed his tune and started doing his chores.

to change the manner of a person, usually from bad to good, or from rude to pleasant. The teller was most unpleasant until she learned that I'm a bank director. Then she changed her tune. "I will help change your tune by fining you $150," said the judge to the rude defendant.

To alter one's approach or attitude.

To reverse one’s views, change one’s mind, switch sides in a controversy. The analogy is very old; John Gower wrote, ca. 1394, “Now schalt thou singe an other song,” and the actual phrase, “change your tune,” appears in a ballad about Robin Hood (one of the Child ballads) from about 1600. And a character in Samuel Beckett’s novel, The Unnameable (1953), says, “I have my faults, but changing my tune is not one of them.”