Yoast provides a great SEO capabilities to WordPress and also Rank Math, here are the steps to automatically generate an SEO description from the post content when posted using WordPress Automatic Plugin

1- On the custom fields section of the campaign enable the option “Add custom Fields”

2- set the custom field name to _yoast_wpseo_metadesc  if using Yoast or rank_math_description if using Rank Math

3- set the value to [gpt3]Summarize this content to 100 words: [matched_content][/gpt3]

4- make sure to use the correct tag in the prompt that returns the post content from the list of available tags displayed

5- Make sure you have added your openAI API key on the plugin settings page for the plugin to be able to process your prompt