@Nep
You get a paper and pencil and start by writing the nouns for everything you can find in your own language translated in your own writing system based on how they sound.
Hold a char in front of her to get her to tell him the word for chair, hold a candle in front of her to get her to tell him the word for candle.
If you can't hold things than point to them. Start with nouns then move onto verbs and more abstract concepts.
If she's not an idiot she should get the idea of what he's trying to do and assist as best she can.
He should then review and memorize as best as possible. There will be some mistakes and misunderstandings but he can just correct them as he figures them out.
He may not be grammatically correct or understand things like cases but he can start off talking like a caveman and figure those things out and take notes as he communicates more.
The more he figures out the easier it becomes for him to ask questions and get clarification.
I don't see any realistic way he could ever learn it if he isn't actively documenting and taking notes.
First priority should be to speak and understand, then if he can do that fluently he could try to figure out their writing system.