What is the process for my first 90-day report in Thailand with a retirement visa, and what documents do I need?

Although I've been living in Thailand for almost a year, I'll soon have to go for my first 90-day report. I used to do everything with a "BORDER RUN," but for the past few months, I've had a "retirement visa."

I know that for a visa extension, you can go three weeks in advance to renew your visa.

Now, I have three questions about this...

1. Can I go two or three weeks earlier? Or does it have to be on the specific date of the piece of paper they stapled to my passport?

2. What documents do I need to have ready?

3. How does it work?

Does anyone have any specific advice? FYI. My immigration office is in Bangkok near Don Meuang apt. I know you can do it online from the second 90-day period onward. But I heard you have to go there the first time.