Hi there,
Go to the Dashboard > Appearance and you should see either GP Hooks or Elements.
If it says GP Hooks then go there and in the before_footer hook you will find the shortcode. Just remove it.
If it says Elements then you should find it in the Elements > Legacy Hooks, just repeat the above.
Finally as i am not sure if this Site has been updated, if it is not in Legacy Hooks then look in Elements and you should see a Element Hook > Before Footer – then you can delete that.