do_action( 'relevanssi_update_options' )
This action hook runs after Relevanssi has set the default options in the plugin install process.
More information
When you install Relevanssi, WordPress runs the Relevanssi install function. It creates all the options Relevanssi needs in the wp_options database table and sets them to their default values.
For a complete list of the options and their default values, see the functions _relevanssi_install() in lib/install.php and relevanssi_premium_install() in premium/common.php (if you have Premium).
This action hook runs after these functions are done setting the default values, so if you want to define your default settings for Relevanssi in code, you can use this action hook to set your option values.