Having a new passport and being out of Thailand when my 90 days expired I have lost my old 90 day report. When reporting my next 90 days will I have to start from scratch, or will they use my details already on immigration's computer be used?

Without the old form (barcode) and with a new TM6 immigration form and last enter date, you will have to fill a new TM47 when you go to immigration, as the old TM6 details on their computer are now outdated

Sent from my CPH1821 using Thailand Forum - Thaivisa mobile app

Leaving the Country resets the 90 day clock.

Your next 90 day report will be due 90 days from and including the date you re-entered.

Your report is due 90 days from when you entered the country.

Immigration can enter your old passport number to find your records of reporting before and then update it with your new passport number and etc. 

Some offices may want you to complete a TM47 form before doing the report.

3 minutes ago, Swiss1960 said:

Without the old form (barcode) and with a new TM6 immigration form and last enter date, you will have to fill a new TM47 when you go to immigration, as the old TM6 details on their computer are now outdated

Sent from my CPH1821 using Thailand Forum - Thaivisa mobile app
 

He should theoretically depending on his location, possibly ensuring a TM30 is filed and transfer his stamps to his new passport before his next 90 day report is due. 

Thankyou all for your advice.