How to pull excerpt from Advanced Custom Field

Hi guys

I am working with the free ‘Boldy’ theme from Site5 (https://wordpress.site5.net/boldy/) which has a predefined excerpt from the_content.

However, I have build a post template that uses the plugin ‘Advanced Custom Fields’ (https://www.advancedcustomfields.com/) and on this template the editor fill in content in the different fields and thereby not in the_content. This means that there’s no excerpt shown for these posts and therefore I want to pull an excerpt from one of the custom fields. I can display an entire Advanced Custom Field by using <?php echo the_field(‘field_name’); ?> but how can I limit the output of this command to only 20-30 words?

Any help would be greatly appreciated ?? Thanks..