How do I go about requesting a 30 day extension following the 60 days given at the airport? Is it done on line ? Can I request it at the airport?

Hi everyone! I got a 60-day tourist e-visa and so arrived in Thailand a week ago. Can I already get the 30-day visa extension at the immigration office now, or do I need to wait for a specific time until I can go to the immigration office to get the extension?

I‘d like to stay 90 days in Thailand in total and would preferably have everything set as early as possible :)

Want to get a 30-day tourist extension next week first thing in the am. Does anyone have a link to downloading the correct TM form? Also, what time does Chiang Wattana open? 8a?

Thx