Check out example codes for "how to change text to bold through script unity". It will help you in understanding the concepts better.

Code Example 1

//Do this for bold
GameObject.Find(/*PutTxtNameHerein""*/).GetComponent<Text>().fontStyle = FontStyle.Bold;

//and this for normal
GameObject.Find(/*PutTxtNameHerein""*/).GetComponent<Text>().fontStyle = FontStyle.Normal;

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