Dell inspiron 15 3000 series how to use a mic from a Handsfree

Hello,
I use dell inspiron 15 3000 series laptop. I attached a hands free set which includes a microphone in it. I want use only the microphone in the hands free set instead of builtin mic due to built in mic is more sensitive to background sounds and it makes me mad. How can I disable the builtin mic and enable the mic in the hands free set
please help me.