En el readme te vienen los pasos
# Download the binary release of ScummVM DS from this page. Unzip the archive into a folder.
# Store your game files into a zip file, making sure to choose the 'No compression' option. If you don't do this, it won't work. If you have more than one game, put them in different folders in the ZIP.
# Check to see whether the games you have are supported by build A or B, using the table of supported games below. You cannot mix games from builds A and B in the same Zip.
# Put the zip file into the directory with ScummVM DS, calling it 'scummdata-a.zip' or 'scummdata-b.zip', depending on which build you're using. Make sure the games will fit on your flash card. The total size off the games cannot exceed 30Mb because of the limitation of the GBA cart bus.
# Double click on the builddata-a.bat or builddata-b.bat as appropriate file to build your ROM image
# Using your GBA flash cartridge software, burn 'scummvm-a-widthdata.ds.gba' or 'scummvm-b-withdata.ds.gba' onto your flash cartridge.