Shows how to update dynamic fields after a signup is submitted

pdb-dynamicfield-update.php

<?php
/**
 * Plugin Name: PDB Dynamic Field Updater
 * Description: updates dynamic fields automatically after a signup submission
 * Version: 1.0
 */

class PDb_Dynamicfield_Update
{
  /**
   * sets up the action
   */
  public function __construct()
  {
    add_action( 'pdb-after_submit_signup', [$this,'update_new_record'], 100 );
  }
  
  /**
   * updates a new record
   * 
   * @param array $record the new record submission values
   */
  public function update_new_record( $record )
  {
    // convert any null values to empty string so they will be updated
    array_walk( $record, function( &$value, $key ) { $value = is_null( $value ) ? '' : $value; } );
    
    // update the dynamic values in the record
    $updated_record = apply_filters( 'pdb-dynamic_db_field_update', $record );
    
    // filter out any values that did not change
    $post = array_diff_assoc( $updated_record, $record );
    
    if ( ! empty( $post ) )
    {
      // if we have changed values, write them to the database
      Participants_Db::write_participant( $post, $record['id'] );
    }
  }
}

new PDb_Dynamicfield_Update();

This needs to be installed as a plugin.

How to Install a WordPress Plugin from a Gist