Oh. I just read your question better. It's the falling sleep that's a problem? I followed a procedure to keep him in his room. Basically I decided that he just needed to stay in his room quietly (this is before he could sleep through the night). So I camped outside his room. And each time he came out, I just guided him back to his bed. No noise, no interaction, be very neutral. After 5 nights, he stayed in his room.

My doctor told me melatonin is ineffective past 6mg. There are other things to try.
1.) White noise. Try turning on a small fan prior to bedtime. It could be as simple as this. The constant whir of the fan is a comfort to some. This has worked for kids I know.
2.) Start a simple nighttime routine... Dinner, teeth, quiet activity, warm bath, etc. Whatever it may be, do it all in the same order every night. You can do this over a few weeks, adding one thing every couple days, until it's established.
3.) If the current bedtime routine you want to change is one in which your child needs to be held, he may need pressure, in which case a weighted blanket at bedtime may be your solution. If it's about security a beloved toy may be a fitting replacement for your presence.

Feel free to message if you are going to try any of this and/or have questions. I would be happy to help if I can.

What has work for myself is a routine. My daughter is 2, but every night around the same time she gets really irritable. I know it's time for bed. Every night at the same time i bathe her, put her to bed. Like someone else said I turn a fan on. I turn all the lights and tvs off so she knows its bedtime. At first it was difficult to get my daughter to bed i see with her a steady routine does wonders!!!

I have found the Choiceworks app helpful. I copied Daniel Tiger's bedtime routine on YouTube. I like that we are squeezing "read a book" in almost every night now- he usually doesn't want to read.

This service is very inconsistent. My son received both the assessment and treatment from our naturopath. But more times than not, I see Neurotherapy offered by a few psychologist. Search on neurotherapy, neurofeedback, or biofeedback. Interview them and find out if they serve the autism population and what their results have been.