Add plugin metods for my plugin

Hey! I wanted to ask how to connect the plugin to the library and use it? I understand the API and I know how to use it. But my situation is different. There is a plugin that is self-written and is not available on the Internet, I need to get a method from this plugin, for example. The player enters the command / hp and his hp is added to the GUI menu / hpgui where he shows his head and his hp. So. I want to connect this plugin to the library and in my plugin, when I enter a new command (create my own, let's say now there will be no health, but hunger) when entering a command, the player's hunger is also added to this menu. That is, I want to get a method for adding player data to a menu that is written in another plugin. Tell me how to do this, please?

 

@Veyn12
Unless the other plugin is publicly available and includes an API I'm afraid you're out of luck.

 

that is, apart from how to rewrite the plugin itself, nothing will help?

 

@Veyn12
That's my guess. You can always contact the plugin author to discuss access to alter their code, or use an API.