Hi,
You can add:
<author> SPDX-FileCopyrightText: Copyright (c) year name_of_copyright_holder email_of_copyright_holder SPDX-License-Identifier: GPL-3.0-or-later </author>Note that this is not specific to GPL. Whatever license you use, you shall make it known. There are several possible ways to do it. I would recommend following the SPDX format. It's simple to manage and you can use the reuse tool to help you ensure you have all what is needed in your software sources.