Help with activation

Help with activation

I bought a used 5x ladt week not realizing it was the international version. So it'll work on wifi and T-mobile, but not on us cellular or sprint. So I bought a brand new nexus 5x, North American edition, from Google. With the phone, they srnt another sim card. Can i just use the sim card ftom my first 5x or do I have to use the new one? If I put in the new card, do I activate it right from the 5x?