Start with a strict GFCFSF diet. Google for more info. .
How do the diet help parents and family ?
Hope you are doing well. In the initial stages there might be some confusion and u might feel lost. I would like to share my experience. And this opinion is solely based on my experience. 1st step would be acceptance of the diagnosis. Learn more, there are plenty of books and information available online.
2nd start early intervention as soon as possible. Get assessment done and see where your child is lacking and focus on building on those skills.
3rd see who are the experts in ur area. And plan to get trained under them, at the end of the day u are the one who spends most of the time with kid.
There are many therapies n diets available. But see what's best for your child. Many options doesn't mean it will all work out fine for your kid.
Hope this helps. Stay strong.