Reinstalling a belt on an electric snow thrower
Based on the way the spring is oriented on the idler pulley B, my guess is that it's meant to pull downward on the belt when it's installed, so the belt probably goes like this:



The exploded parts diagram in the owner manual (on the page you linked to)  shows the belt in this same orientation:



There might be a slot or hole in the idler pulley assembly that would let you pry it back with a screwdriver or other tool while you slip the belt on the main pulleys.

When the machine jammed with ice, the auger may have stopped and the belt may have been damaged if the motor was still spinning. Look for signs of cracks, worn down spots, etc both on the belt and the pulleys. If you can't find an exact replacement belt (part number PJ670 - 56663-024 on the parts diagram), a small engine repair shop may be able to find an equivalent replacement.