Increment the complete lesson count in a custom field

increment-lesson-count.php

<?php

// todo change hook to the one in your LMS
add_action( 'lesson_completed', 'increment_lesson_count_custom_field' );

/**
 * Increment the lesson completed count of the logged in contact
 * Todo add any relevant arguments to the function
 *
 * @return void
 */
function increment_lesson_count_custom_field() {
	// Get the contact record of th current logged-in user
	$contact = \Groundhogg\get_contactdata();

	if ( ! $contact ) {
		return;
	}

	// todo change to your custom field
	$key = 'lesson_count';

	// Increment the count
	$contact->update_meta( $key, $contact->get_meta( $key ) + 1 );
}