he meant he had no more idea than you what happened .... disconnect the cable from the speedo and pull out the inner part and clean it well with solvent, get it totally dry and lube it with dry graphite .... but that won't put the needle back on the speedo

you need to take the gauge cluster out, remove the speedo and see just what happened there, if the needle came off the shaft or the shaft broke .... you'll likely find a lot of gunk build up in the speedo head that got petrified in the cold, clean it out carefully
Bill