mypmpro-update-user-countries.php

<?php
/**
 * This will update all member's billing country to Germany.
 * 
 * Exercise caution when making these changes. They cannot be undone. Make a backup of your database
 * before running this script. 
 *
 * Enter /wp-admin/?updateusercountry=true in your URL to run the script. 
 *
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

function mypmpro_update_users_country(){

	//run /wp-admin/?updateusercountry=true
	if( isset( $_REQUEST['updateusercountry'] ) ){

		$users = get_users( );
		
		if( $users ){

			foreach( $users as $user ){

				$meta = get_user_meta( $user->ID, 'pmpro_bcountry', true );
				
				if( $meta !== "" && $meta !== "DE" ){
					//Not empty and not in Germany, update
					update_user_meta( $user->ID, 'pmpro_bcountry', 'DE' );
				}
				
			}

		}

	}

}
add_action( 'admin_init', 'mypmpro_update_users_country' );