Users in MIUI forum has informed that the JIO preview offer is now available for RN3 users.
You will have to install all the apps and open myjio and open get jio option to continue registration. Install ALL the JIO apps available in myjio and open myjio and open get jio option to continue registration. If you are already using any JIO app, clear all data first.
However, as experienced by Samsung users, the offer may not be available for all locations.