Here's how you can raise a dispute on the Fi app:
Tap on the 'Pay' section of the homepage
Tap 'All Transactions'
Choose the transaction against which you'd like to raise a dispute
Tap 'UPI Help / Get Help'
Tap 'Raise Dispute'
Answer a few questions related to the dispute
Tap 'Submit'
For any further queries, feel free to contact our customer care team via chat or write to us at help@fi.care.