, go to website of immigration bureau, then go to Online Appointment. What services are available for online appointment are immigration office specific.
, the first 90-day report after you enter Thailand again is supposed to do in person.
You can try online (15 days before until 7 days before the due date) first, somehow some people get their first reports after travel out of Thailand approved online (may or may not be glitch). If not approved, go on in person.
Thank you for the report. Yes, online appointment works pretty well at Bangkok offices.
When you have to do a 90-day report "in person", you can do it by registered EMS through Thailand Post (not all offices accept by post though, Bangkok does) stamped dated 15 days before the due date.
The 90-day report doesn't require the applicant's attendance at the immigration office but the original passport has to go, you can ask your family or friend.
, (editted) what you uploaded is the requirements list for a short-term extension based on Clause 24, visiting Thai family for 60 days. This extension can be applied only once per visa/visa-exempt. And this doesn't require proof of funds of 400K baht.
If you want to apply for a long-term, 1-year extension based on being a family member of a Thai national, you need a requirements list for clause 18. This requires proof of funds.