Now as we’re replacing the apn file, we’ve to overwrite the existing file
We’ve to restore the “Permissions” as before
To do this, Long Press the apns-conf.xml file and select “Permissions”
Check the boxes as shown in the first screenshot above. The Octal value should be 0644. Select OK
Open Phone dialer and dial ##3282#
Select “APN Settings”
Click on “3 dot icon” on top left corner and select “Reset to default”
Now insert your GSM sim and go to Settings<More<Mobile Networks<APN Settings.
The apn settings of your GSM sim should be visible. Select it and start using cell phone data.
Please let me know if this has worked for you or not via the comment section below.