How can I help my language exchange partner improve?

As a native Japanese speaker, I understand how difficult it can be to reach a point where you can speak the language freely. I take my English studies seriously, and I want to help my language exchange partner if they are serious about learning the language. The problem is that they are overconfident and unwilling to listen because they finished a basic textbook and now think they can talk about anything. They can't understand me when I speak basic Japanese. Their Japanese writing makes no sense because they omit vowel sounds and use particles incorrectly. At their current level, having a conversation is overwhelming. Japanese is harder than they expected. I suggested we review a textbook together, but they refused, saying that Japanese people don't normally speak like a textbook. I don't know why they think this way. When I asked them which style of Japanese comes most naturally to them, they couldn't answer. I have a straightforward question: How can I help my language exchange partner improve their Japanese proficiency?