Ethernet card died; replaced but cannot make 'internal"?

Hi there,

Very simply (I hope) question with an equally simple answer...in my dreams.

Basically I had one network card fail within my office Untangle machine, it was the one assigned as "internal".

I replaced the card, and Untangle rightfully recognizes the new card...I deleted the old card within the interface which was no longer physically in the machine...expecting to re-assign the new card as 'internal'.

But I cannot figure out how to do just that? Is it possible? Please help I will buy you a beer!