Factory reset Samsung Galaxy S3 without screen
You could use recovery mode and guess the controls from resources available online or you could use adb if u had developer options enabled and type:

adb shell
--wipe_data


EDIT: I read the comments on your question and it looks like if u wanted to reset it you can go into recovery (Home+VolumeUp+Power) and then press volume down twice and then press power and then press volume down 6 times and then press power again.