You don't need to enable VoLTE. Insert the Jio (VoLTE enabled) in any slot. By default, VoLTE will be active. If it is not, you can change the network preferences from Network option in settings.
Alternatively, you can follow a much easier way:
You can check the below video to get more clarity:
Specs: Xiaomi Redmi Note 5
Yes, Both the sim slots in the device comes with 4G network support across all broadcasting networks in the country. It also provides VoLTE functionality.
To check all the other details of the device through this link Xiaomi Redmi Note 5
It takes around 2 hours to charge the Redmi Note 5 fully.
Specs: Redmi Note 5
SAR value of Xiaomi Redmi Note 5 is yet to be determined as the device is not yet out.
You can check all the other details of the device using this link Xiaomi Redmi Note 5