I'm not certain what your intention is, but if the instance name of the textfield is name1, then you can assign its text using:
name1.text = "123";
If you have an array of the instances, the same applies, so long as the array is assigned the instances and not string versions of their names.
var txt:Array = new Array(name1);
txt.text = "123";
If you have an array with strings of the instances names, then you need to use bracket notation to have the strings interpretted as instances...
var txt:Array = new Array("name1");
this[txt].text = "123";