How to set focus in a text fiels

I have an input text box, the var = input text.( created at design time )
I wish for this to have focus - just as if someone had clicked inside the box.
That is, when the Time line enters the frame where the text fld is the text field has focus.

so. How does on set focus ?

( is this going to be a situation where it can only have focus set if it was created at run time ??? )