How to edit that is inside datafolder

I made a DataFolder with

@mkdir ($this->getDataFolder());
$this->database = new Config ($this->getDataFolder()."data.yml",Config::YAML,[
"blue" => "player"
]);
$this->db = $this->database->getAll();

What code should I use to edit "player" to playername?

 

PHP:

$this->db["blue"] = "new player name";

// And this code saves it to disk:
$this->database->setAll($this->db);
$this->database->save();