How to backup older files

I lost my phone and I got a new one. How will I do to find older backup for my Iphone. I have backup with Timemachine.

When I connect my iphone to itunes it only finds one backup file (and it is my wifes backup) in my computer. I have backup files on external disk, but how do I find the right file? Which file is mine or my wifes?

Thnx