Check out example codes for "how to change textMesh Pro unity". It will help you in understanding the concepts better.

Code Example 1

GetComponent<TMPro.TextMeshProUGUI>().text

Code Example 2

// If you are trying to chnage the text on a TextMeshPro:
  
public TextMeshPro TextMeshProObject;
//you shouldnt need to get component the editor should take care of this for you when 
//you drop it since you have the object set to TextMeshPro and not just GameObject
TextMeshProObject = GetComponent<TextMeshPro>();
TextMeshProObject.text = "Hello";

// If you are trying to change the text from a gameobject:
TextMeshProUGUI TextMeshProLable = YourGameObject.GetComponent<TextMeshProUGUI>();
TextMeshProLable.text = "Your Text"

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