それなら

Beginning a sentence with それなら provides a meaning of "if so", "then", or "if that's the case." It references a previous statement and usually goes on to provide some sort of response on it.

A: 今夜、どこかおいしいレストランで食事したいと思っているんだけど。
B: ああ、それなら、新しくできた和食レストランに行ってみたら？なかなかおいしかった。
A: Tonight I think I want to eat at a good restaurant...
B: Ah, then why don't you try going to the new Japanese restaurant? They were pretty tasty.

それなら、リーさんは指輪を買って、アリスにあげたほうがいいね。
If that's the case, Lee-san should buy the ring and give it to Alice.

両親は毎日のように、よく勉強していい大学に入りなさいといいます。それなら、私が勉強している時、弟や妹に静かにするように言ってほしいと思います。
Almost every day my parents tell me to study well to get into a good university. If that's the case, I think I want to tell my little brother and sister to be quiet whenever I'm studying.

それなら全て捨てていきたい。
If so, I want to through everything away. (from Ayato's lovely "Addicted" song)