Look for Football Manager Editor. You should be able to find it in Steam, under Tools in your library. Then, you'll need to load the DB and you start editing as you like and saving changes to use in new saves.
You can even look in youtube, there's plenty of videos for older versions of the...
I create a new country replacing Andorra where I create two divisions, twenty teams, each one represents country and the players are the biggest legends from that country.
First Division:
- Portugal
- England
- Brazil
- Argentina
- Netherlands
- Italy
- France
- Spain
- Soviet Union
- World...