To install the files in the correct place. go to where My Summer Car is installed, usually is:
C:\Program Files (x86)\Steam\steamapps\common\My Summer Car

Looks for a Folder called: Unity_Assets_Files. If you can't see it, create a new folder called   Unity_Assets_Files

Open the Cherry_Blossom_Gauges.rar then into the Cherry_Blossom_Gauges Folder. There will be two folders, sharedassets1 and sharedassets2.

Drag and drop both these folders into the Unity_Assets_Files folder.
(this will be for the cherry blossom gauges with no suski picutre)

From there you will need to download Texture Pack Importer Tool, here: 
https://www.racedepartment.com/downloads/texture-pack-importer-tool.17294/
there will be instructions where to put the tool on there.

Once you have install Texture Pack Importer Tool.
run: TexturePackImporter.exe
Press Enter on your keyboard, wait for the program to tell you to press Enter again.

Hopefully that should all be fine and dandy. :)