You need a file extractor to download this game on your mobile. Install the zarchiver app to install and extract the files.
First, download the GTA San Andreas APK + OBB files onto your device.
Second, launch the zarchiver app and navigate to the download folder, where you will find apk and OBB files.
Thirdly, click on the apk file and tap the install option. There is a message asking you to allow installation from the zarchiver app. Just allow it. When it is done, do not open the game.
Fourthly, move back to the download folder and find the OBB file there. Click on the file and then click on the extract option. Now open the android folder and navigate to the OBB folder. Click on the downward arrow. Once the extraction process is complete, you can open the game and play it.