Use RSDKTool on your PC to extract Data.rsdk into loose files. Then, repack it into a new RSDK that the Android decomp expects. Some deconversions require a specific filename: game.rsdk or Data.rsdk. Check the README.
Search GitHub for "ManiaDecomp-android" (look for repositories with frequent commits, ideally by Rubberduckycooly or MysterD). Avoid random APK sites—they inject malware. A trustworthy build will publish the SHA-256 checksum. The best "high quality" variants include:
(Best way to play Mania on Android – if you own the game legally)