Gist to add custom meta field & exdend csv importer to import these fields for location post. Divi Multi Location plugin.

custom-meta-data-field-and-imports-for-multi-locations.php

<?php

// Add custom fields to Location post type
add_filter( 
	'mlsl_custom_fields', 
	function($fields, $container){
			// Add your custom fields by appending to $fields array
			// Fields Documentation  https://docs.carbonfields.net/ (version 3.3.2) 
			
			$fields[] = \Carbon_Fields\Field::make('text', 'my_custom_field', 'My Custom Field')
					            ->set_help_text('Description for my custom field');
	
			return $fields;
		}, 
	10, 
	2 
);


// CSV Import post processing after a single location is created.
add_action(
    'mlsl_location_meta_field_import',
    function($post_id, $data){
    	// Check if my csv data row has 'URL' column
    	if(isset($data['URL'])){
    		add_post_meta($post_id, '_my_custom_field', $data['URL'], true);
    	}
    },
    10,
    2
);