Follow these 4 steps below to download google play store app:
STEP:1
Check Current Version Check the currently working version of your phone's Google Play Store app.
STEP:2
Download Google Play Store Using Apk The non-default version (with respect to your mobile model) of Google play store can only be downloaded in APK file.
STEP:3
Enable Unknown Sources & Install Enabling unknown sources option allows you to install application other then Google play store, which in this case is necessary.
STEP:4
Disable Unknown Sources After installing the Google Play Store app, you are done and now you can again disable unknown sources option for security.