I was lucky that I had an endocrinologist who recognised the symptoms, I had all the tests in hospital for a true diagnosis.
I have had five or six eOGTTs, and I would recommend supervision.
I would also ask what do you wish to achieve from the test? It is usually two hours for type two, or five hours for Hypoglycaemia. Do you want a fasting or non fasting test?
Have you got a glucometer? You will need one and test strips. You need to write down, the readings you get. Pre drink, or fasting, every fifteen minutes or 30 minutes?
Please do understand that the test is hospital supervised.
Keep safe