Separate iphones from the same account

Follow the steps in the link below to remove one of the iPhones from the account:

What to do before you sell or give away your iPhone, iPad, or iPod touch - Apple Support

t157 wrote:

my 6S and 7 are on the same apple account, how do I separate phones?

Go to Settings Tap on your name. Turn off iCloud. Then log in with a different iCloud account, or create one.