JSFiddle - React, Tailwind, and code Playground

HTML

Swap col #<input id="col_1" value="2"> with col #<input id="col_2" value="3">

<br>

<textarea id="input">
A1—B1—C1
A2—B2—C2
A3—B3—C3
</textarea>

<button>Swap</button>

<textarea id="output">

</textarea>

CSS

textarea {
  width: 100%;
  height: 120px
}

button {
  margin: 10px 0
}

JavaScript

$("button").click(function() {
  var text = $('#input').val().split("\n");

  var delimiter = "—";
  var col_1 = $('#col_1').val() - 1;
  var col_2 = $('#col_2').val() - 1;

  var out = [];
  var col_arr = [];
  var col = '';

  // Get first column
  for (var i = 0; i < text.length; i++) {
    col_arr = text[i].split(delimiter);
    col = col_arr[col_1];
    if (col != undefined) col = col;
    else col = '';
    out[i] = col;
  }
  
  text = out.join('\n');

  $('#output').val(text);
});