terebi no rimokon ga mitukaranai node, onryou wo kaeraremasen.

の links two nouns and often works like of or an apostrophe-s in English.

So:

• テレビ の リモコン = the TV’s remote control / the remote control for the TV

Here, テレビ describes what kind of remote it is.
It is not just any remote, but specifically the one for the TV.

In リモコン が 見つからない, the remote is the thing that is not being found.

The verb here is 見つかる, which is an intransitive verb meaning:

• to be found
• to turn up

With 見つかる, the thing that is found takes が.

So:

• リモコン が 見つからない = the remote can’t be found / I can’t find the remote

Even though the English translation often uses I, Japanese does not need to say I here.

This is a very common question.

There are two related verbs:

• 見つける = to find (transitive)
• 見つかる = to be found / to turn up (intransitive)

So:

• 見つけない = do not find
• 見つからない = is not found / cannot be found

In natural Japanese, when something is missing, people often say 見つからない rather than 見つけない.

Compare:

• リモコンが見つからない。
  = I can’t find the remote.
  (literally: The remote isn’t turning up)

This sounds very natural when something is lost or missing.

Both can translate as can’t find, but the nuance is a little different.

• 見つからない
  = it isn’t found / it won’t turn up
• 見つけられない
  = I am unable to find it

So:

• 見つからない focuses more on the item not turning up
• 見つけられない focuses more on the speaker’s inability to find it

In this sentence, 見つからない sounds very natural because the remote is simply missing.

ので means because, since, or so.

In this sentence:

• テレビのリモコンが見つからないので、音量を変えられません。
• Because I can’t find the TV remote, I can’t change the volume.

ので gives a reason in a slightly softer, more explanatory way than から.

Compare:

• 見つからないので… = because I can’t find it…
  (more neutral/explanatory)
• 見つからないから… = because I can’t find it…
  (a bit more direct/conversational)

Both are possible, but ので fits well in polite speech.

を marks the direct object of the verb.

Here:

• 音量 = volume
• 変える = to change

So:

• 音量 を 変える = to change the volume

That is why 音量 takes を.

This is because 変えられません is the potential form of 変える.

• 変える = to change
• 変えられる = can change
• 変えられません = cannot change

So:

• 音量を変えません = I will not change the volume
  (a choice or decision not to)
• 音量を変えられません = I cannot change the volume
  (lack of ability/means)

In this sentence, the speaker is not refusing to change the volume—they are unable to because the remote is missing.

Here it is potential, not passive.

• 変える = to change
• 変えられる can sometimes look ambiguous, but in this sentence it clearly means can change

So:

• 音量を変えられません = I can’t change the volume

A passive reading would not make sense here.

Japanese often leaves out subjects when they are understood from context.

In English, you usually need to say:

• I can’t find the remote
• I can’t change the volume

In Japanese, if it is obvious who is speaking, you can just say:

• リモコンが見つからない
• 音量を変えられません

The listener naturally understands that the speaker means I.

リモコン is a very common shortened word in Japanese. It comes from:

• remote control

In full Japanese-style loanword form, it would be something like リモートコントロール, but in everyday speech people almost always say:

• リモコン = remote

This abbreviation is completely normal.

The comma marks a pause between the reason and the result:

• テレビのリモコンが見つからないので、
• 音量を変えられません。

It helps readability and makes the sentence easier to process.
It is similar to pausing after Because I can’t find the TV remote, ... in English.

The comma is very natural here, though Japanese comma usage can be more flexible than English punctuation.

Yes. The sentence you have is polite because it ends with ません.

Polite:

• テレビのリモコンが見つからないので、音量を変えられません。

Casual:

• テレビのリモコンが見つからないので、音量を変えられない。

Or even:

• テレビのリモコンが見つからないから、音量変えられない。

These all mean roughly the same thing, but the tone changes:

• ません / です style = polite
• plain form = casual

The sentence breaks down like this:

• テレビのリモコンが = the TV remote
• 見つからないので = because (I) can’t find it
• 音量を = the volume
• 変えられません = cannot change

So the full structure is:

• [Reason] テレビのリモコンが見つからないので
• [Result] 音量を変えられません

This is a very common Japanese pattern:

• Aので、B。
• Because A, B.