textasset and how to use them

So i was making my first game in unity. I was using a .txt file to store dialogues, I have script that reads it line by line and add to list so I can use them later.But apparently the way I was reading that text file doesn't work after building the application. I've read that I need to use textasset, however i could't find any clear informations on how to use that function. Here is code I was using:

 struct DialoguLine
     {
         public string name;
         public string content;
         public string[] options;
 
         public DialoguLine(string Name, string Content)
         {
             name = Name;
             content = Content;
             options = new string[0];
         }
 
     }
 
     List<DialoguLine> lines;
 
     void Start () {
         string file = "Assets/data/dialogue.txt";
 
         lines = new List<DialoguLine>();
 
         loaddialogue(file);
     }
     
     // Update is called once per frame
     void Update () {
         
     }
 
     void loaddialogue(string filename)
     {
         string line;
         StreamReader page = new StreamReader(filename);
 
         using (page)
         {
             do
             {
                 line = page.ReadLine();
                 if (line != null)
                 {
                     string[] lineContent = line.Split(';');
                     if (lineContent[0] == "player")
                     {
                         DialoguLine nextline;
                         nextline.name = lineContent[0];
                         nextline.content = "";
                         nextline.options = new string[lineContent.Length-1];
                         for (int i = 1; i < lineContent.Length; i++)
                         {
                             nextline.options[i - 1] = lineContent[i];
                         }
                         lines.Add(nextline);
                     }
                     else
                     {
                         DialoguLine nextline;
                         nextline.name = lineContent[0];
                         nextline.content = lineContent[1];
                         nextline.options = new string[0];
                         lines.Add(nextline);
                     }
                 }
             } while (line != null);
             page.Close();
         }
     }

So here comes my question, how can I add this txt file as textAsset(this question may seem stupid to you but I honestly don't know and was unable to find any explanation) and how to change this code to make it work? BTW Sorry for bad english