Update 2020-04-20 : My more recent experience is not as great as described below: GDPR-R20191223-1354 asking to correct my email address was confirmed 2020-01-17. On 2020-03-02 I had to sent a reminder. On 2020-03-25 I finally got the reply SE was legally not allowed to process my request. I asked for clarification 2020-03-26, again no response (now waiting almost a month). Sharing this such others may enter the process with realistic expectations. I hope this will be fixed soon.
My personal experience as of Dec 2019 with requesting (SE wide) removal of my (other) account via the contact form, selecting the Other topic, was a swift reply asking me to use the Submit a Data Access Request form.
My experience with that form was very positive. It was completely handled within minutes:
