How do you convert bsnl 3g sim to 2g sim?

To convert a BSNL 3G SIM to a 2G SIM, you need to visit a nearby BSNL customer service center or retailer. Bring your ID proof and the existing 3G SIM card. Request the conversion to a 2G SIM, and they will provide you with a new SIM that supports 2G services. There might be a nominal fee for the new SIM, and activation could take some time.