Pre-populate Caldera Forms field based on slug

pre-populate-cf-field-slug.php

<?php
/**
 * Pre-populate First Name field if user is logged in.
 */
function filter_caldera_forms_render_get_field_first_name( $field, $form ) {
	$current_user = wp_get_current_user();

	if ( is_user_logged_in() ) {
		$field['config']['default'] = $current_user->user_firstname;
	}

	return $field;
};
add_filter( 'caldera_forms_render_get_field_slug-first_name', 'filter_caldera_forms_render_get_field_first_name', 10, 2 );