"用对话表达" can be translated into English as "express through dialogue" or "convey through conversation".
Here are some example sentences to illustrate its usage:
We can express our thoughts through dialogue.
(我们可以用对话来表达我们的想法。)
The author effectively conveys emotions through conversation in the novel.
(作者在小说中通过对话有效地传达了情感。)