hi I have a apple watch I bought that in kijiji canada but I dont know

hi I have a apple watch I bought that in kijiji canada but I dont know

i dont know that the previous owner disnt remove his apple id now i cannot pair on my iphone and i cannot use it.do u have any idea how to remove the apple id so i can use it.i already did the unlock code tru serial number but still i can see the previous apple id.please let me know and how much thanks