Opposite of "mute" or "silence" as verb

Solution 1:

For televisions and similar appliances unmute is an acceptable word that is in common usage.

For silence meaning subdue I would choose encourage as an antonym .

Solution 2:

Despite what your dictionary might say (or not say),

unmute

is a perfectly acceptable word to describe that action. There are many combinations of affixes that are productive on many roots which just aren't mentioned in word lists.

Solution 3:

Oh, there won't be a special word. So many people watch tv with others, there's only one remote. We'd all be using it if there was such a word.

reinstate is a single-word that could sometimes be used.

In the context of the tv scenario, I'd just say put it back, or turn the sound back on, or something. I certainly wouldn't unmute it.