To Block your RBL Bank ATM Card open the mobile banking app → Login → Manage Debit Cards → Select your Debit Card → Tap on Block. The bank will block your card immediately.
This was just a short answer to your query. But I will explain other methods to block RBL Bank ATM Card as well. In case you have lost your card somewhere. Then you should take immediate steps to block the same. This is very important to avoid unauthorized transactions and misuse of the card.
You can also make use of the internet banking facility of the RBL Bank to block your card. In case you are facing any kind of difficulties then call the customer care immediately. And never share your details like the PIN Number with anyone. The bank officials will never contact you asking for such details.