Need to add wp_remote_post

Hello there,
I have installed wordpress on my university server. I have added Generate Press theme to it and it works. I cannot update it however. The site ( https://docs.generatepress.com/article/license-key-activation-issues/ ) advises me to use wp_remote_post function. The problem is I have no idea in where I should run the code (in which file). I am not familiar with php at all. I would really appreciate if someone could help me out.