How do you handle returned goods in e-shopping? The blockchain is immutable. So, using bitcoin for shopping websites can cause problems. Customers often want to return purchases in retail scenarios. But Bitcoin is immutable, so we can't reverse the transaction.
Somebody please guide me how to handle the problem of returning goods in bitcoin-based e-commerce.
Questions like this are off-topic on this forum, however I'll take a stab at answering your question as you seem to have a lot of misunderstanding.

The bigger question you need to ask yourself if why you want to implement your e-commerce application on a 'blockchain'? It would be a gross neglect for basic engineering design principles as blockchain is nothing but a slow and expensive database. I mean I would understand if you wanted to create a Dapp if you are selling drugs and other illegal substances (like SilkRoad) since you wouldn't want a single point of failure and lack of attribution as an owner. However, if you are creating an e-commerce application that is perfectly legal you can create it on a normal database system.

Blockchain is one of the many components that make Bitcoin successful, not the only one. A blockchain is used in Bitcoin to prevent double spend attacks as transaction included in previous blocks get precedence over the latest transaction if they spend the same output, and achieving consensus on a global scale where all participants have the authority to accept changes.

Private blockchain is nothing but an old wine in a new bottle. There are plentiful example of distributed databases with multiple write access available today like Google Spanner or Paxos. So, coming back to the question you need to ask yourself, what are benefits that the "blockchain technology" is providing you that is not possible with existing 'traditional' solutions in the market?