I have lost books

Hi there,

I think my problem is common.

I  tried to transfer books between two devices.  Because I don't remember any IDs I couldn't open some of the purchased books on the second device.

After I returned to my first device the same books were also "broken".  I couldn't restore them.  I think I have different books with different "users".
I have no clue how to restore them.

What can I do?

Many thanks