Here's one way to disable the mic, albeit a bit long-winded.
– Click on the start button,
– Type in 'Settings'.
– Select 'System', 'Sound'.
– Scroll down and click on 'Manage Devices'.
– Scroll down to 'Input devices'.
– Click on your Mic, it will expand and you should have the option to Disable/Enable.
I have a mute button my keyboard Neil, does yours have a function key combination for Mute?
Ed.