Welcome to the Bunnings Workshop community @nafisa. It's wonderful to have you join us and many thanks for your question.
Is your question about the fresh growth that is curling, or are you after general citrus care advice?
Citrus leaves can curl when a disease is present, temperatures are too cold or too hot, or an insect infestation such as scale, mealybug, mites or aphids. Over or under-watering can also cause citrus tree leaf curl.
Try opening some curled leaves to see if any insects are living inside them. Pest oil will take care of most insect infestations. Apart from the curled new growth, your citrus looks rather healthy and should only need some fertiliser every six months. You should find this guide useful: Growing Citrus Plants.
Please let me know if you need further information or had questions.