Select the selected attachment when open gallery media.

select.js

  // open
_media.frame.on('open',function() {

// add class
_media.frame.$el.closest('.media-modal').addClass('acf-media-modal acf-expanded');

//console.log( _media.frame.state() );

// set selection
var selection	=	_media.frame.state().get('selection'),
attachment	=	wp.media.attachment( id );


attachment.fetch();
selection.add( attachment );

});