Would like to bulk populate a custom field via CSV import - php

Question

I have a custom plugin and it includes an import/export section. I have added a new ACF field called serial_number_issued. I would like to bulk populate this using a CSV import file. However, I'm not too sure what I need to add to the code to get this working. I've added serial_number_issued to the list array but what do I need to add to update the page:
list( $system_name, $system_id, $status, $serial_number, $serial_number_issued ) = $data;
$status = ( $status == '-' ) ? 'Generated' : $status;
$status = ( ( $status == 'Generated' ) && ( $system_id != '-' ) ) ? 'Allocated' : $status;
// If serial exists, update. If not, insert new
$post = get_page_by_title( trim( $serial_number ), ARRAY_A, $sha_wreg_module_slug );
if ( isset( $post['post_type'] ) && ( $post['post_type'] == $sha_wreg_module_slug ) ) {
$serial_id = $post['ID'];
// Update system info
if ( ( $system_name != '-' ) && ( $system_id != '-' ) ) {
$system = get_post( $system_id );
update_post_meta( $serial_id, $sha_wreg_prefix . 'system', array( 'id' => $system->ID, 'name' => $system->post_title ) );
}
// Update status
update_post_meta( $serial_id, $sha_wreg_prefix . 'status', $status );
This is the page with the Serial Number Issued column that I want to update with the CSV file import
So we want to be able to bulk update the field with the answer Yes.
Here is the full code for the import.
switch ( $action ) {
// Import cards from CSV
case 'import':
if ( isset( $_FILES[ $sha_wreg_prefix . 'import_csv' ] ) && ( $_FILES[ $sha_wreg_prefix . 'import_csv' ]['error'] == 0 ) ) {
$row = 1;
if ( ( $handle = fopen( $_FILES[ $sha_wreg_prefix . 'import_csv' ]['tmp_name'], "r" ) ) !== FALSE ) {
while ( ( $data = fgetcsv( $handle, 1000, "," ) ) !== FALSE ) {
$row++;
if ( $row > 2 ) {
list( $system_name, $system_id, $status, $serial_number, $serial_number_issued ) = $data;
$status = ( $status == '-' ) ? 'Generated' : $status;
$status = ( ( $status == 'Generated' ) && ( $system_id != '-' ) ) ? 'Allocated' : $status;
// If serial exists, update. If not, insert new
$post = get_page_by_title( trim( $serial_number ), ARRAY_A, $sha_wreg_module_slug );
if ( isset( $post['post_type'] ) && ( $post['post_type'] == $sha_wreg_module_slug ) ) {
$serial_id = $post['ID'];
// Update system info
if ( ( $system_name != '-' ) && ( $system_id != '-' ) ) {
$system = get_post( $system_id );
update_post_meta( $serial_id, $sha_wreg_prefix . 'system', array( 'id' => $system->ID, 'name' => $system->post_title ) );
}
// Update status
update_post_meta( $serial_id, $sha_wreg_prefix . 'status', $status );
wp_update_post( $serial_id . 'serial_number_issued', $serial_number_issued );
} else {
$data = array(
'post_title' => $serial_number,
'post_type' => $sha_wreg_module_slug,
'post_status' => 'publish'
);
$serial_id = wp_insert_post( $data );
// Update system info
if ( ( $system_name != '-' ) && ( $system_id != '-' ) ) {
update_post_meta( $serial_id, $sha_wreg_prefix . 'system', array( 'id' => $system_id, 'name' => $system_name ) );
}
// Update status
update_post_meta( $serial_id, $sha_wreg_prefix . 'status', $status );
}
}
}
fclose($handle);
}
$_SESSION['sha-wreg'] = array(
'class' => 'notice-success',
'message' => 'Serials successfully imported'
);
}
break;