Note: If you decide to switch your version of Sonic Mania to this version and then attempt to submit a run, you must use the other leaderboard used for the Unpatched/v1.03 versions of this game (at the time of this guide being posted) found here: https://www.speedrun.com/sonic_mania_pre-dlc

1. Exit out Steam first, then right-click on Steam shortcut and click on Properties.
2. Under where it says "C:\Program Files (x86)\Steam\Steam.exe" (the text box next to Target), add '-dev -console' after. It should look like this: "C:\Program Files (x86)\Steam\Steam.exe" -dev -console
3. Hit Apply and OK. Quit out of Properties.
4. Open Steam as Administrator
5. You'll see the Console be added at the big tab menu: STORE LIBRARY COMMUNITY (username) CONSOLE
6. Click on Console, then type down this command: download_depot 584400 584401 3856100003260477365
7. Look at the text in the prompt. When it downloads, it will give a directory of where it is. Use that directory to find these three v1.03 files:
8. data.rsdk
9. SonicMania.exe
10. steam_api.dll Paste these to the Sonic Mania directory (I would recommend making a backup of the original files before doing so) and you should be set.