How do I pick which mic to use for RINGR Desktop?

When you connect to a call in RINGR desktop, you will be prompted for microphone permissions:

Click 'allow' so that the app can read and remember this setting. Afterwards, the audio input selector will be displayed - on subsequent calls you may not be asked for permissions again, but you will be asked to select audio input and output settings for every call:

If you need to change your audio input/output settings, close the call window and re-join the conversation.