Obviously teachers meet a lot of students on a daily basis and may not have total recall about everything they have told every student. However it is good that you should mention the fact that the teacher has already informed you of a fact or related some similar information to you previously.
I learned that in a previous lesson, can we move on to the next lesson?
Can we try another lesson since I have already learned this one?
I've already done this lesson, may we do a different one?
Most teachers are open to teaching new things. Saying you have already learned something could offend some people but if you add a suggestion about doing another lesson it softens the request. You don't want a teacher thinking you didn't want to learn something or were being lazy. So requesting a different lesson lets them know you still want to learn something just not something you already learned. Questions are also easier to be accepted than statements.
I learned that in a previous lesson, can we move on to the next lesson?
Can we try another lesson since I have already learned this one?
I've already done this lesson, may we do a different one?
大抵の先生は新しいことを教えることについて寛大です。「もう習いました」と伝えると気を悪くする人もいるかもしれませんが、別のレッスンの提案をすれば、よりソフトにお願いにできます。先生に勉強したくないとか怠けていると思われたくはないですね。別のレッスンを提案することで、学びたい気持ちはあって、単にもう既に習ったレッスンをしたくないだけだと伝わります。また、質問の方がステートメントよりも受け入れられやすいです。
I learned that in a previous lesson, can we move on to the next lesson?
（それは前にレッスンで習いました。次のレッスンに進んでもいいですか）
Can we try another lesson since I have already learned this one?
（他のレッスンをしてもいいですか、これはもう習ったことがあるので）
I've already done this lesson, may we do a different one?
（このレッスンはもうやったことがあります。他のをやってもいいですか）
If you are wanting to tell someone you have already learnt something then it's always nice to be polite so as not to upset them 'I learnt that last time' or 'I have already learnt that' these would be a good way to do this
それはもう習ったことがあると伝えたいなら、相手を怒らせないように丁寧に言った方がいいです。次のように言えます。
'I learnt that last time'（それはこの前習いました）
または、
'I have already learnt that'（それはもう習いました）
"I have already learned about that." can be used when you want to tell your teacher that you were taught a particular topic, grammar point, vocabulary, etc. before.
"I have already learned about that."（それはもう習いました）は、特定のトピック・文法・ボキャブラリーなどについて、「前に教えてもらいました」と先生に伝えたいときに使えます。
Native speakers will often say "I learned this last time" when referring to something that they studied before. This term is used to express not wanting to study that topic again and a desire to move on to something else. Adding "last time" at the end of the sentence makes the situation very specific to the last lesson they had.
If a native person wants to explain that they studied something sometime before but don't want to give a specific time frame, they would say "I learned this already" instead. Another natural way that a native person can express that they studied something in a previous lesson would be to say "I studied this last time".
ネイティブスピーカーは、既に習ったことがあることについては、よく "I learned this last time"（これは前回習いました）と言います。これは、「それについてもう一度勉強したくはない」「次に進みたい」という気持ちを表します。文末に "last time" を加えると、習ったのがその前のレッスンだったことが明確になります。
具体的な時期を示さずに既に習ったことを伝えたいときは、ネイティブスピーカーなら、代わりに "I learned this already"（これはもう習いました）と言うと思います。
もう一つ、前にレッスンで習ったことがあることを伝える自然な言い方として、"I studied this last time"（これは前回習いました）もあります。
The most correct way to respond in this case is with "I learned that last time." If more formality is needed, replace "last time" with "in a previous class." Also if you are getting somewhat exasperated, then it would be more proper to say, simply, "I know," or "Teacher, I already know this!" That last one I would only recommend if you had the same online teacher as before.
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