1. Put "ievanpolkka.resource" & "IevanPolkka.exe" in My Summer Car root folder ( SteamLibrary\steamapps\common\My Summer Car).
2. Execute "IevanPolkka.exe" rewrite the asset file according to the instructions (path to the files is My Summer Car root folder).
Changed the 2 files "topless_gun" (ID: 2552 AudioClip & ID: 3089 MovieTexture) in sharedassets3.assets and added "ievanpolkka.resource" audio resource.
I'm sorry for being unfamiliar with MOD production and publication.
Because machine translation is in English, the words may be wrong... SUMIMASEN m(_ _)m