Bolder, 36, replaces Mark Hume, who departed the club earlier this week.
Hume replaced Bolder in November 2017 when he left the Seadogs after four years to take up the managerial role at then National League North side, North Ferriby.
He said: "I'm absolutely delighted to be back. Scarborough's a fantastic, forward-thinking club with everything in place to do well.
“I’ve continued to follow how they've been getting on and have been to some games. Having had a year in management, I know that experience will help in my role with Steve and the players.”
Bolder was sacked by North Ferriby in October after overseeing a poor start to the EVO-STIK Premier Division, though the Villagers remain rooted to the foot of the table despite the change.
He played in the Football League with Grimsby having come through the youth ranks at Hull City, and also had spells at Ossett Town and Guiseley.
Manager Steve Kittrick said: "I'm really pleased Chris has agreed to come back and I introduced him to the players at training last night - plenty know him already from last season.
"He's learned a lot from his time as manager at North Ferriby and having him back will be a big plus for us.”
Scarborough, who have lost six of their last eight league games, are in action at home to Hednesford Town on Saturday.
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