How can I set the first line indent is 0, according to the boxed text

Try this,

function boooxed (object_style_name) {
  if (app.selection.length !== 1) return
  var doc = app.documents[0];
  var sel = doc.selection[0];
  if ('baseline' in sel) {
    var bx = sel.insertionPoints[0].textFrames.add();
    bx.appliedObjectStyle = doc.objectStyles.item(object_style_name);
    bx.geometricBounds = [0,0,5,30];
    sel.duplicate(LocationOptions.AT_END, bx.parentStory);
    bx.insertionPoints[0].firstLineIndent=0;
    bx.fit(FitOptions.FRAME_TO_CONTENT);
    if (sel.contents.length) sel.remove();
  }
};

var object_style_name = "AAA"; //set anchored object settings, textframe preferences, and more
boooxed(object_style_name);

Vandy