sorry if I do some errors because I can’t speak fluently english 
use any gta img tool in the play store and open gta3.img in Android/ data/ com.rockstargames.gtasa/ files/ texdb/ gta3.img and click on the 3 points in the top at the right
and select add files with replace and select any dff file

for the textures you need to install an txd tool apk and after that open it, click on the folder icon and select gta3.txt in Android/ data/ com.rockstargames.gtasa/ files/ texdb/ gta3/ gta3.txt
and select the file icon after that you need to select txd archive and select any .txd files