Follow the below steps:
Go to Contact and tap the contact you want to have video call with. Then tap the video call icon on the right side of the contact.
Note:
1. Both parties need to support the VoLTE(4G Calling) function and video call function.
2. VoLTE needs to be activated for you by the network carrier.
3. VoLTE needs to be enabled on your phone.
4. VoLTE needs to be supported by your local network.
5. Both of you need to be in the same VoLTE network (Jio and Jio, Vodafone and Vodafone).