So your field group is either created in a plugin or somewhere in the theme. You can either modify the theme or you can add a filter to set the default value. I would go with the filter, you can add this to your functions.php file.
I can tell by looking at this that it’s either a repeater field or a flexible content field and you’re going to need the field key in order to add the filter so you’ll need to find where the fields are created to get the field key.
What version of ACF is being used? You’ll need to search for where the fields are created and that may be a bit different depending on the ACF version.
