You can’t. The sdl options are restricted compared to the Windows version due to limitations of the Android platform. Magic Dosbox will always run at your device’s native resolution, and display the game without scalers by default. I think what you’re looking for is the “Filter” option. Press the back button when Daggerfall has launched, then tap “Filter”, and chose one. IIRC, you’ve got an S7 edge, so you should be able to use “5xBR lw” just fine, or at least hq2x.