Bower had previously led the Avenue to two successive play-off finishes but returns with the club second-bottom after an 8-0 defeat to Brackley Town on Saturday.
He was replaced by Garry Thompson in the summer who lasted just two games of the new season before Marcus Law's interim spell in charge.
And Bower told the club's official website that it won't be a walk in the park to change their fortunes.
"I’m really pleased to be coming back. There’s no denying its a big job," he said. "We are where we are and have to be realistic, there’s no magic wand. It’s going to take a lot of hard work to turn it around.
"“It wont be easy. We will have some dark days but can’t dwell on those. We have to get everyone together, and work to get out of the bottom Two. The target is to stay up”
Bower also issued a rallying call to the club's supporters, saying: "We need your support more than ever. We’ve had some great times as a club over the past few years, with good wins and hard fought points, often times that been down to the ‘Twelfth Man’ effect.
"But now we need everyone to come together and fight for the Avenue, both on the pitch and in the stands."
Bower will have a while to wait for his first game in charge with his side not in action until October 12 when they welcome Hereford to the Horsfall.