how would i unlock an carrier lock off iphone se

MY DEVICE SUSPOSE TO BE UNLOCK, BUT WHEN I HAD PUT MY SIM CARD INTO MY IPHONE SE, IT INDICATED THAT NOT A VALID SIM. NEXT I HAD WENT TO THE SETTING ON THE IPHONE TO SEE WHAT CARRIER IT WAS ON AND I DIDNT SEE ANYTHING. SO IS THERE SOMETHING THAT IM MESSSING OR DOING WRONG