The 27-year-old left the club - who are also known as Anambra Warriors - in November, having rejected a lesser role after he had led them to the 2016 Nigerian FA Cup.
He has made a dramatic return following the exit of his successor, former Accra Hearts of Oak manager Kenichi Yatsuhashi, who left the club last month with the board citing "unprofessional conduct".
Former Ghana international forward Yaw Preko has been in temporary charge of the side following the exit of Yatsuhashi.
Everton, the youngest manager to win the Nigerian FA Cup at 27, returns with Brazilian player Alberico Barbosa da Silva who also helped the team to fourth place in the Premier League last season.
FC IfeanyiUbah, who have a partnership deal with English side West Ham and play in the same colours as the Premier League club, will face Egyptian club Al Masry in the Caf Confederation Cup first round next month.