double voice record problem

I am new on Cubase so I don’t really know how everything works…
I’ve got it on a mac and i’ve got a sound card for my “extern” microphone.
Everytime when I say something in my “extern” microphone it records but when I am too close to my pc, the mic of my pc Registers my voice as well wich gives a double sound effect.
I have tried to disable the mic of my pc but then my “external” microphone doesn’t want to record as well?
Can someone please help me?
Thank you!