Properly matching your team formation, tactic, and players' playstyle can activate Formation Combo.
How well your players have mastered a particular playstyle will determine how effective your Formation Combo will be. You can make your Formation Combo even more powerful by improving the skills and abilities of your players.
As for the acquisition of the Formation Combo, the manager may bring it to a team.
The usable Formation Combo depends on the team manager. Select HR> Member List, and induct the manager who has the Formation Combo you want to use.