you need to add m_controller so it can see it. Usually, by passing it into the function, but this has a GUI flavor to it, so you may instead be able to add it to the current gui class.
take note: if you can't see this here, you probably also have not set or managed the boolean that it is affecting. It may not be in a good state.
Notice all the other functions in that file look like: voidxmrig::App::onConsoleCommand(char command)
They are in the xmrig namespace, and belong to the App class.
You'll also need to modify the corresponding header file that presumably defines the App class.