How to change fragment’s textView’s text from activity

You can find the instance of Fragment by using,

For support library,

YourFragment fragment_obj = (YourFragment)getSupportFragmentManager().
                                              findFragmentById(R.id.fragment_id);

else

YourFragment fragment_obj = (YourFragment)getFragmentManager().
                                             findFragmentById(R.id.fragment_id); 

Then create a method in the Fragment that updates your TextView and call that method using fragment_obj like,

fragment_obj.updateTextView();