I am the lawful guardian of my child but her father live in other country.. he want to see his child.. my child being an american I have consent to send her back to his country ,but I am wondering if he don't send her back at all... what would I be able to do about it... because it's a different country
What can I do to get her back

Has she left yet?
If not, maybe he should do the travelling..

You probably won't be able to get her back, at least not easily. A woman from the Middle East wrote a book about how she lost her daughter this way, and went through all sorts of headaches and heartaches to get her back.

Ask him to visit your daughter in this country. (How old is your daughter?)

There is often little you can do, esp if the other nation does not respect or honor any ruling of a US court, And they do not have to. And in some nations, women have little or no rights at all in court.

So no, unless he wants to just send her back, there is little you can do to get her back normally