Potty training autistic toddler

My son just turned 3, he is in the spectrum. Says a lot that I don’t understand and just a few words. Doesn’t respond when called or call when he needs me much as he can say mummy. Now sure if he knows am called mummy. Anyway. He is 3 and still in diapers. Any tips on potty training? I tried months ago and he refused to sit on the potty so I put it away. I don’t even know how to communicate it.