How do I know what region to set a DVD drive to?

I just plugged a DVD player to my Mac Pro, and put a DVD in. The DVD starts playing in Viewer, then a message pops up asking me to select a region because the region set to the DVD doesn't match the region set to the drive. It says I can only select a region five more times. I think this player is one I bought from China over eBay some years back. How do I decide which region to set the drive to? I'm not sure which region to set this drive to.

I found this documentation by Apple on this topic. The message box doesn't allow me to set the region to 0, which is a setting that allows the drive to work with all regions, according to the chart in the documentation. Change your DVD drive region in DVD Player on Mac - Apple Support

The message says that the drive is currently set for region 1, which is North America. The DVD allows for a selection to show in different languages. I actually bought it while here in the U.S. from an organization in the U.S. It has worked on other DVD drives on a PC.