I’ve used the following code for the main posts page
<?php
$text = get_field('text', get_option('page_for_posts'));
if( !empty($text) ): ?>
<?php echo $text?>
<?php endif; ?>
How do I change this for the custom post archive page? Or do I need to use a different method?
I don’t understand why your are asking. Is the code not working? Since you are getting a value from a specific post (i.e. get_option('page_for_posts')
) your code should work wherever you place it in your templates.