brush up on

To improve, refresh one's knowledge of something

提高，重温某人在某方面的知识;温习

I must brush up on my French before going to Paris next month.

下个月去巴黎之前，我必须温习一下法语。

He hasn't studied English for so long that he'll have to brush up on it. 他很久没有学英语了，所以他不得不重新学习提高一下。