That’s what computers are for. Go to Google and do a Keyword search–power of attorney australia should do, or legal forms australia. What you want is a “revocable power of attorney” so you can cancel it, and make sure its force is limited to buying property in your behalf to be deeded in your name. I presume. Download it, have a Singapore lawyer review and witness it, and send it (I don’t know the legal status of a fax in either country; sorry).

Don’t be a cheap charlie and save peanuts for a home purchase by DIY. A wrongly worded POA may cause you to lose your option payments. Go through lawyers. Ask them who are the experts to include POA for a modest fee.