Normally, you should be able to switch between the European and North American region by clicking the Earth icon at the top of your PLAY button after logging in.
If this doesn't work, you can manually override the launcher setting to select the NA servers by doing the following:
- Go to C:\Black Desert Online
- Scroll down until you find the launcher config file
- Open it and change for region from Europe to North America (or the other way around)
It should look like this:
Then save the file and launch the game. This should fix your issue.