Depends on the province you want to enter. Phuket for example give you three options: a) vaccination passport, b) covid-free-certificate or c) rapid-test for 500 Baht. The rapid-test will be replaced with quarantine from the 15th this month.
Well... he asked the same question in "Phuket Expats", so i guess Phuket, but maybe he just try to find the answer in any available group...
For the Form here... not sure it was labelled with Phuket or not, but i remember that the backside was a copy of a bank statement from a swiss guy... i was a bit jealous about the amount in his account... ;-)