You can change the slug from oum-location to something else with this PHP (add it to your theme’s functions.php or use a Code Snippet plugin):

function my_oum_location_custom_slug( $args, $post_type ) {
    if ( 'oum-location' === $post_type ) {
        // Change 'new-location-slug' to whatever slug you want
        $args['rewrite']['slug'] = 'new-location-slug';
    }
    return $args;
}
add_filter( 'register_post_type_args', 'my_oum_location_custom_slug', 10, 2 );

After adding the above code, go to Settings → Permalinks in the WordPress admin and simply click “Save Changes” to flush the rewrite rules. You don’t need to change anything else, just saving the page once will flush the permalinks.