GDPR data request

Hello,

when trying to export the personal data of an user I get the message:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, class ‘PieRegister’ does not have a method ‘register_my_plugin_exporter’ in C:\xampp\htdocs\…\wp-includes\class-wp-hook.php on line 288

When I try to export the datas then I get an error message.

The data export is necessary for GDPR-compliance. What is to be done about it?

Regards, Johannes