as far as I can tell you have to apply for that visa outside of Thailand at an embassy/consulate then enter Thailand with it…with this visa you can apply for the 1 year retirement visa inside Thailand…are you in or out of Thailand
the 90 day report is a self explanatory system on the 90th day or so you go to immigration or apply online or mail it in, no additional documents are needed all there do is look you up in the system to make sure your visa is still valid
Fly into Cambodia (figure out their COVID related entrance protocols) complete the Thai pass with everything that it requires…fly into Singapore, fill out Thaipass with all requirements