HELP! How do you reduce the mic gain on the bluetooth

The mic gain is up to high and when my wife talks on her bluetooth you can hardly understand her because its almost distorted because the mic gain must be adjusted to high. I've heard of a trick to get into the maintenance screen(upper left, lower left, upper, lower...trick) but I can't get it to come up. I must be starting in the wrong screen or touching the wrong area or something. If any one knows very specific step by step procedure it would be nice. Thanks, 2005 model