play by ear
verb1
Of music To play guided by one's musical perception and intuition, rather than from a written score.
2
Idiomatic To do by guessing, intuition, or trial and error; to react to events as they occur, often with risk of negative outcomes; to improvise.
- If they ask for something we didn't prepare, we will have to play it by ear.
- There over, hereunder / Or up above, don't wonder / We can always play by ear / But that's the deal, my dear2001 August 30, Shakira, “Whenever, Wherever”, in Laundry Service: