School refusal autistic teen GCSE year

Seeking some advice with how to get an autistic teen who is due to sit his GCSEs this June with school refusal. He is extremely bright but is currently struggling with accessing school. They have agreed to reduce some of the stresses on him such as requirement to completing  non essential homework but I am really concerned that he may not return in order to sit his GCSEs. He won’t talk to anyone about what his anxieties are. Has anyone any advice or can offer any help?