Welcome to Flyertalk arunbijapur.

Unfortunately, this is a policy that airlines across the industry have adopted. You must fly your trip as you've booked it - skipping any part of it may cause the remainder of your trip to be cancelled.

Your best option would be to contact your travel agent and see if they can change your ticket to the dates you want.

Otherwise, cancel your ticket and see if you can use that credit to book a new trip.

Finally, another idea may be for you to keep your trip as it is now and book a separate journey BLR-BOM-BLR for the dates you need to be in Bombay.