It just snaps back in but it was a very tight fit and took two people to force it in. Plus I had no instructions and hadn't seen it before it broke so it took a little time to figure out where it was supposed to go. The arm doesn't connected to anything except the rack. I guess water just shoots up into it from below.
The dishrack came in one box I opened the box snapped on the rollers and the bumpers and put it in the dishwasher, could not have been easier Thank you partselect