Depending on the procedure
meet the one treating you to see if they are a good fit for you.
If they seem nice and willing, find something where you can both agree to make it better for the both of you.
If you can notify them ahead of time, mention your needs.
“I have autism which might contribute to my discomfort.
What can I bring to the clinic? Can I leave my pants on, or can I wear a skirt instead of having to undress?
Can you prepare smaller medical tools?
Do you have sedatives?
Are numbing agents readily available?
Do you have a room with an adjustable seat?
What’s the best treatment for me?
Are there other options to make it easier to get care?”
Look up pictures of the place, visit it, read any rule policies and see if they can accommodate to getting special permission for certain aspects.
Get a personalized treatment plan.
Mention you’ve special needs regarding X.
Use telemedicine, an appointment over video, phone call or text chat, when available and appropriate.
Ask about at home tests you can send.
Tell your doctor about your worries.
They might be able to help you address them.