Odoo v10

How to run migrate scripts? How to migrate Odoo between minor versions. For example between version 4.12.2 to 4.12.3?

I read https://odoo-development.readthedocs.io/en/latest/maintenance/data-migration.html 

I created directory called 'migrations' in my custom app and I created directory called 4.12.3 There I created python file called pre-migration.py:

def migrate(cr, installed_version):
    print(cr)
    print("======================================================")
    print("ooooooooooooooooooooooooooooooooooooooooooooooooooooooo")
    print("======================================================")

I ran server and my migrate scripts didn't run. I saw in logs that my custom module was loaded, but migration scripts not. How can I run them?