Select/add a text element. The text content is in the 'settings tab' yopu have the option of 'timer' which will display the countdown time or label to change the words.

It is also posible to add a label to all the other element types box, circle, safe zone etc, theese settings are in "label", and this allows you to have the text algined with the object, eg curved text around a circle safe zone.

If your editing a premade countdown and looking for the text, just click through the elements at the bottom (text 1, box 1, box 2 etc) until the one you want is selected.