Go to file theme.liquid, find the tag that contains cart information (in header). It"s similar:
If <li> tag has ID please remember this ID. After completing installation, pleasego to Settings-> Styles and update this ID into the field: Mini Cart element ID wrapper
If ID does not exist, please add the id="sca_fg_cart_target" into this tag. In the other themes, the tag may be <div> or <span> tag.