YOU SAID:

I think I finished it and how.

INTO JAPANESE

私はそれを終えたと思うし、どのように。

BACK INTO ENGLISH

I think I've finished it and how.

INTO JAPANESE

私はそれをどのように終えたと思います。

BACK INTO ENGLISH

I think that's how I finished it.

INTO JAPANESE

私はそれを終えた方法だと思います。

BACK INTO ENGLISH

I think that's how I finished it.