This is a Thai form. My experience renewing my Belgium passport in Thailand the Belgium embassy gave me a letter stating the reason for issuing. They told me immigration would require the letter. Which they did. I stated this before and many people have thanked me as they needed it also.
The easiest way is to go to a visa agent. Yes it will cost you but everything will be done. No worries. It is true you can do it yourself for a lot cheaper but you probably end up fustrated. From the second year do it yourself very easy then
The first priority is filing a police report for lost documents. The next important is your passport as you will not be able to get a new bank book(passport) without passport. I renewed my Belgium passport a few years ago and when they issued a new passport they gave me a letter stating the reason for the new passport which immigration required. With the new passport and letter everything was in order with immigration for them to stamp the new passport.
As per previous comment it really sounds like you are confused about expiry date and 90 day report. You can only do a 90 day report when you have a valid visa or visa extension. In your case this expires Mar 15.