How unlocked my i phone 6 s
I buy used iphone in this iphone when i install my sim its not working because of country code
iPhone 6s
See Change your Apple ID country or region https://support.apple.com/en-us/HT201389 See this heading especially What to do before you change your country or region
Use this link in the document if you need to View
your Apple ID balance https://support.apple.com/en-us/HT202359
Contact Apple SupportIf you can't complete any
of the steps, can't change your country or region, or you have less store
credit than the cost of a single item, contact Apple Support.
Note that you could just purchase something of value greater than or equal to the amount of your store credit.
And you also can contact iTunes
worldwide support via text or chat using this link https://support.apple.com/choose-country-region/itunes