To set a resolution for Bluefin Ultrawide signage players, simply visit https://www.thebluefin.com/downloads and scroll until you see Video Mode Plugins for BrightSign Presentations.
Select the plugin for the desired resolution. and download it. Then, open BA Connected and access the SD card using DWS and place the file in the Videomode directory (requires Carousel for Brightsign version 2.0.3.0+).
Then simply reboot your player.