YOU SAID:

I had to read this again once I read it.

INTO JAPANESE

私は一度それを読んだら、これをもう一度読まなければならなかった。

BACK INTO ENGLISH

I had to read it once, once I read it.

INTO JAPANESE

私はそれを一度読んだら、一度それを読んでいなければならなかった。

BACK INTO ENGLISH

Once I read it, I had to read it once.

INTO JAPANESE

一度それを読んだら、一度それを読まなければならなかった。

BACK INTO ENGLISH

Once I read it, I had to read it once.