Q: apple id set up my phone i forgot

apple id forgot,                                                                                                                                                                                                                                                                              first i updated my ios8 in my phone after i updated ios8 my phone ask for my apple id on first set up on my phone.now unlocked my phone with out my first apple id i forgot.how can i fine my first set up apple id i forgot                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              christopher,