Not able to setup mobile data in Apple watch series 4

Hi,

My friend got me Apple watch 4 series from US and i am using it for a while now and have made an attempt to enable mobile data in the watch and when i select Mobile data option from my watch app in phone i see this message" This Apple watch does not support Airtel mobile data in this region. Apple watch can only be used with data plans that are certified by your network provider, and your region".

I use Airtel as mobile data in my phone.

Please guide how to proceed further to enable this option ?

Regards

Venkatesh