Hi Kevin, there are three ways you can apply for an Autopass Card, online, at Tuas or Woodlands Checkpoint, or at the LTA Customer Service Centre, the easiest being the online application.
This is the link for applying for it online. You will need your Identity Card/passport,
your work pass/residence pass issued by the Singapore Government (if any),
a valid vehicle insurance certificate (for foreign vehicles not registered in Malaysia, you must have motor insurance from a Singapore-based insurance company to cover your vehicle while it is in Singapore), and a vehicle registration certificate (if it is not in English, an English translation is required). Hope this helps!