How can I apply model method on records that already exist on server through console?

How can I apply model method on records that already exist on server
through console?

The issue that my application is already alive and bunch of user's use
data, in which I found bug and fixed it in the code. But how can I modify
their data with edited method, which is actually is before_save callback?
I have their input for this record stored in another column, I need to
modify output.
How I can do this?