What to do when running into a linguistic hallucination?

I'm using an app powered by a fine-tuned Qwen 2.5. There’s a specific word for my work that I use frequently, but it isn't in the model’s vocabulary. It keeps breaking the word apart or hallucinating a different meaning. Very frustrating.

Since I'm using the app and can't retrain the model myself, what are the best ways to "force" it to learn this word?