It is not 083 or the Nigerian code 234; these are phone dialing codes.Owerri has a post code of 460.You can find out from the post office in Nigeria
What Is The ZIP Or Postal Code For Owerri, Capital City Of Imo State Of Nigeria?
460
083. Or better yet, put it together with the country zip code +234(083)
460001
083. Or better yet, put it together with the country zip code +234(083)