You'll connect the Ice Cream Mixer attachment to the same location as the other beaters, but I'm sure you know that :) The mixer attachment does have a plastic top outer facing -- I'm not sure if you're referring to it as the disc? If so, it stays above the beaters and slightly under the connection. Does that even make sense?
Or, could the disc you describe be a temporary plug? I hope you get it figured out fast so you can enjoy some ice cream.