Add seconds to a countdown - Android

Question

I wish that when a button was clicked, 10 seconds would be added to my timer, but I couldn’t find a way to add value to Countdowntimer, here’s my code.

private void contagemRegressiva(){
    new CountDownTimer(31000, 1000) {

        public void onTick(long millisUntilFinished) {
            tv_tempo.setText("Tempo restante: " + millisUntilFinished / 1000);
        }

        public void onFinish() {
            tv_tempo.setText("Tempo esgotado");
        }
    }.start();