Panasonic Quintrix sound problem/channel scan?

Recently my Panasonic Quintrix F began to have no sound on certain channels, roughly about half the ones I subscribe to via cable.

When I called for help on this problem, I was told simply channel scanning will help the problem.
However, no matter how hard we look, we cannot find any item under menu that will allow a channel scan.

Anyone know how I might fix this problem, or simply can tell me how to find channel scan?