How do I remove the previous gmail ID from Lollipop after a hard reset?

[AC Question]

how do i remove he previous gmail ID from lollipop after hard reset??

i performed a reset to android device because of locked by incorrect pattern attempt by my friend..after finish, In the starting its asking me to log in from the gmail used on this device previously,,and i can't remember that even i flash that device with odin with its firmware...but still same problem
anybody can please help me about that?????