Download a file manager app (like ZArchiver) if your phone doesn't have a good one. Extract the OBB file (if it's in a .zip or .rar format).
: If you own the game on PC, you can stream it to your Android device for free via the Steam Link App NVIDIA GeForce NOW Euro Truck Simulator 2 Apk Obb Download For Android
If your PC is turned on and running the game, you can use the free Steam Link app on Google Play to stream ETS2 directly to your phone over Wi-Fi. Download a file manager app (like ZArchiver) if