Hi there, Thanks for getting in touch with us. It seems there are some issues on your database that is why the option to add enquiry form fields is not appearing. So kindly add the below code in the functions.php file of your current active theme on your site –
add_action('init', 'fix_catalog_issue');
function fix_catalog_issue(){
delete_option('mvx_catalog_pro_enquiry_form_data');
}
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After adding this code refresh the Enquiry form settings page and you will get the option to add form fields there.
After this you can remove the code from the functions.php file.
Let us know if you need any further assistance from our end.