You probably have noticed that many mods which i share here may have the first step to "Import textures or replace dff files in gta3.img" to do that its important for you to extract the obb data of GTA San Andreas mobile, usually the steps requires computer but those who don't have a pc can use there phones to extract the obb files.
Before You Start
Extracting obb files of GTA San Andreas Android can take a lot of time depends on your smartphone specs.
All files like "gta3.img" and others img files are inside main & patch obb
Make sure you have 2.5GB of Free Space in your internal storage as new smartphones wont let you mod in your SD Card due to limitations
I recommend using ZArchiver for extracting the obb files.
The file you edited should to there according folder. for example if you replace something on gta3.img then move it to Android/data/com.rockstargames.gtasa/files/texdb as in obb it was located in texdb folder. (create a new folder if it doesn't exists)
Tutorial How to Extract OBB Files Using Your Smartphone or Tablet
1. Before Proceeding you need to locate the obb files which can be found in Android/obb/com.rockstargames.gtasa/ <here>
2. Change extension of both files from ".obb" to ".zip". You can do that by simply writing .zip at the last of there names. for example name of the first obb file is "main.com.rockstargames.gtasa.obb" rename it to "main.com.rockstargames.gtasa.obb.zip"
3. After doing the above steps your .obb files are now converted into .zip files, now open them one by one and click extract and choose location where to want to extract them (internal storage if you are on Android 11 or above)
Note : I recommend creating a folder name GTA Modding inside your internal storage and do all the modding work inside that folder.