Help PLS! Blacklist Removal

my grandmother had lost her phone (iPhone 😎 on a trip, so my aunt reported the lost phone to her at&t insurance and they sent her a new phone. My grandmother eventually found the phone before coming home, so my aunt stored the old phone to give to me as a gift, once i had the phone i tried putting my sim in it, turns out the phone is blacklisted is there any way to  unblacklist the phone so i could use it.