What should my brother do about his TM-30 and 90-day reporting before he leaves Thailand?

Just so EVERYONE is clear about the 90 day reporting

This is how it works

IF you are INSIDE thailand on the date a 90 day report is due (as in you have NOT left the country during the previous 90 days) you REPORT, period, end of story

The window of opportunity to report IN PERSON is from 2 weeks before the due date to 1 week after the due date <- that does NOT mean if you are leaving thailand within the week after your report is due you don't need to report.

So, let me state it one more time so people catch on; IF you are in the country when a 90 day report is due, YOU REPORT...

Also though it should go with out saying I will say it, IF you exit the country on or before the 90 day due date when you come back in the 90 day count down clock starts over and your next 90 day report is due 89 days from the date you stamp in

and yes, when they come back they need to file a NEW TM30 because the online 90 day report system and the TM30 system are cross-linked so they check the address you use with the latest TM30 filed and if it's a different address (like you stayed in a hotel somewhere in the country then they will reject the 90 day report as the address doesn't match the TM30 on record)

He needs to do his 90 day report before he leaves Thailand. It was due yesterday as you stated.

IF he does not, then after he returns to Thailand, the next time he needs a service from Thai Immigration, he likely will be fined 2,000 Thai baht for not filing his 90 day report when IT WAS DUE.

GO get the stamps moved, get the re-entry permit, FILE a 90 day report in person and if needed file the TM30 (and take the 800baht fine for failure to file on time)

you are slightly confused

there is no "grace period" if you're leaving thailand 😕 that 7 days after is IF you are filing in PERSON, not flying out within a week from the due date