Welcome to the Bunnings Workshop community @Ramkumar. It's great to have you with us.
We'd love to help you revive your tree but need a lot more information to assist. Can you please share some photos of your tree and tell us more about it such as how old it is, whether there have been any recent changes, what type of soil it is in, how much it is watered, whether you have been feeding it, etc.
You might also like to search for the words lemon and citrus on the site as you'll find other members have received great advice in the past to help nurse struggling trees back to good health. Bunnings also have the helpful guide How to grow and care for a lemon tree
We look forward to reading more about your tree and about all your projects and plans for around the house and garden. We're sure you will get plenty of helpful information, advice and inspiration from our amazing community members.