Navigate to the Toolbox by clicking the hamburger menu icon in the top right corner.
Click "Tuner" in the Toolbox menu.
The default setting of Tuner is muted (click to unmute). The Tuner range can be set between 430Hz and 445Hz (the default value is440Hz).
*If the Tuner can't detect the input signal, please go to Settings -> Audio Setting and make sure the input is selected as Mono.