说到某个问题，我得干某事了。。。。翻译英语。

不对，

Talking about ...., I have to do something.

例如，

Talking about homework, I have to complete it by tomorrow morning.

说到作业，我明天早上之前要完成。

比较地道的说法：
By the way , I should (have to) go ...

翻译为：顺便说一下，我要...

用于在一件事正在进行的时候突然插入别的事或改变话题。

Talking about an issue, I have to do certain things. . . .