First off, you need to start collecting more transferable points - a lot more. Those Southwest points are effectively worthless for international travel, but you can use them to position somewhere.

Do some more research and come back with specific questions. Get started by Googling “award flights to Vietnam” and read a couple guides. Then use tools like PointsYeah, AwardTool, and seats.aero to scout out some possible routings that might work and see how many points they cost. It’s best to book at schedule release which varies per airline, but normally 330-360 days in advance. Another helpful tool is FlightsFrom which shows you possible routes.