change the voice

Whose voice you want to start with, grandma or I?

AnonymousMy grandmother had told me a story before I went to bed

If you put a full stop at the end, it will be correct.

Anonymous My grandmother had told me a story before I went to bed

I imagine you're asking about changing your example into the passive voice:

My grandmother had told me a story before I went to bed. (active)
I had been told a story before I went to bed by my grandmother. (passive)

JohnS

Anonymous My grandmother had told me a story before I went to bed.

Passive 1: A story had been told to me by my grandmother before I went to bed.
Passive 2: I had been told a story by my grandmother before I went to bed.

CJ