Step 1: speak to your GP
Book an appointment with your GP. Make sure your diagnosis is the only thing you are seeing your GP about. If you try to mention it during a consultation about another subject, your GP may not address it fully.
Step 2: present your case
Your GP needs a reason to refer you for diagnosis, so you will have to explain why you think you could be autistic, and how a diagnosis would benefit you. If you think you might want help with this, ask someone you know to come with you.
Does anyone know where I can get a assessment for ADHD or Asd