find one's voice

(idiomatic) To become willing or able to talk or otherwise express one's opinions

Example: 2015, Louise Taylor, Papiss Cissé and Jonny Evans spitting row mars Manchester United’s win over Newcastle (in The Guardian, 4 March 2015)[1]
  The biggest cheer of the night came shortly afterwards. St James’ Park finally found its voice to welcome back Jonás Gutiérrez into a Newcastle side for the first time since his diagnosis with testicular cancer 17 months ago.