Here's the link to the immigration web page to do it - no need to register - you can do it 7 to 14 days before the due by date. A day or two after you submit it you will be emailed and a new report by date will be available on the link you that you can print off and keep
I went to Koh Chang for a month in April, I have not notified CW that I returned to BKK in May, but my landlord filed a new TM30 on my return and again two weeks ago when I moved to a different apartment in the same condo.. Do I also have to report to immigration before doing my extension next month? (Marriage )