how do I add link script to gameobject that already exist with attached script

Questions & Answers
1

Without creating a new gameobject and without specifying name of gameobject That already exist
something like

ClassAnother nameofTheInstance = this.gameobject.GetComponent(ClassAnother);
2

adding another script to an object doesn’t make sense. You can just call the script or it’s functions by:

ScriptName other1;

Start() {
      other1 = GetComponent<ScriptName>();
}

Update() {
      if (other1.goldCoins == 17) { other1.goldCoins = 99; }
}
//short for ScriptName.GetComponent<ScriptName>().goldCoins;

Unless you’re creating a new object, and need to add the script, then:

createdGameObject.AddComponent<ScriptName>();