The former Boro player and coach departed midway through last season to take up the manager's job at North Ferriby United, but he is now back as Steve Kittrick's right-hand man following the departure of Mark Hume.
"It was a quickfire situation. I spoke to the gaffer on Thursday night, I was delighted to get the call and I was delighted to get the chance," he said.
"This is a fantastic club, one that I've spent time as a player, a coach and then an assistant manager.
"The fans are amazing and so is the infrastructure.
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"I know the club well, I know the players well and I also work well with Steve because we both have good respect for each other.
"It was a tough decision to leave in the first place, but it was from a personal development point of view.
"I feel that in my time at Ferriby I have developed from all sides. The 14 months I spent there was like 10 years.
"It was a case of dealing with confidence in players, issues with players and recruitment.
"We also had to create an unbelievable team spirit, which had to be the best in the league because our backs were against the wall when it came to budgets.
"I got to tactically pit my wits against some great managers in the Conference North and the Evo-Stik Premier as well, which really brought me on as a coach."
Bolder is now turning his attentions to helping Boro out of their current drop in form.
He added: "Hopefully I can play a part in initiating an immediate change.
"I have experienced it in the past. People sometimes don't understand the psychological side of the game, you don't lose your technical ability as a footballer overnight.
"You have to have the confidence to play, which is something we will be looking at.
"If the fans were offered this start to the season - in the play-offs at Christmas - a few months ago then I'm sure they would be pleased with how things were going.
"I think we still have a chance of achieving big things this season."