Just entered Thailand from abroad, but 90 day check-in form says I must check in next week, is this date reset to date entering Thailand?

Yes. 90 days from when you last entered.

When you exit Thailand you due date for 90 day reports evaporated.

Your next due date is 90 days from your entry date.

 

If doing online reporting remember to change the "enter date".

You can still use autofill and then just edit the entry date. 

Thank you all for confirming.

Yes, 90 days starts again upon entry.