What do you mean by ‘edit the settings’? Do you mean, there is no ‘Custom Fields’ menu item to edit the field groups? If so, perhaps the developer has hidden the menu item with some code in the functions.php file or added the constant for ACF_LITE. These are 2 common ways of removing the menu item.
If you can’t add an image, it is most likely you have a JS error on the page. Open your console log and look for errors on page load and on button click.
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