<?php if( have_rows('repeater_field_name') ): ?>
<?php $i = 1; while ( have_rows('repeater_field_name') ) : the_row(); ?>
<?php the_sub_field('sub_field_name'); ?>
<p>ID <?php=$i; ?></p>
<?php $i++; endwhile; ?>
<?php else : ?>
<?php endif; ?>