How do you insert a Post variable into the form?

I have a button that comes from a product page and want to have the contact form 7 add the ID as a value to a field normally empty (I am sending the variable as POST already).

I would prefer to use post variable instead of get variable, but I won’t complain if there is only a get variable solution.

I believe the thread bolow covered this issue, but it is outdated and I would prefer not to edit the plugin file and lose changes when updates come along.

https://ww.wp.xz.cn/support/topic/contact-form-7-input-fields-values-as-php-get-viarables?replies=33

Any help would be appreciated.

https://ww.wp.xz.cn/plugins/contact-form-7/