"Ievan Polkka" (Savo Finnish for "Eva's Polka") is a popular Finnish song with lyrics written in the early 1930s by Eino Kettunen to a traditional Finnish polka tune.
It is also known as "Loituma's Polka" (or "Loituma's Polkka").
1. Put "IevanPolkka.exe" in My Summer Car root folder. (SteamLibrary\steamapps\common\My Summer Car)
2. Put "ievanpolkka.resource" in Data folder. (mysummercar_Data)
3. Execute "IevanPolkka.exe" rewrite the asset file according to the instructions. (path to the files is My Summer Car root folder)
Change the 2 files "topless_gun" (ID: 2552 AudioClip & ID: 3089 MovieTexture) in sharedassets3.assets and added "ievanpolkka.resource" audio resource.
※Manual installation is time consuming & mistakenly risky, so if you have a lot of requests, I will write it again.