The phrase "kick button" means to take action or make things happen in a quick and powerful way.
Sentences with «kick button»
To perform this technique press kick button after jumping into the air. (gamepur.com)
After filling up the V - Trigger gauge, you can unleash every character's special attack by pressing the heavy punch and heavy kick buttons. (softpedia.com)
The punch and kick buttons do exactly what you would expect while the slash and heavy slash buttons utilize your character's weapon. (darkstation.com)