You can reset or change the UPI PIN by following below steps - 

1. Launch your Fave app 

2. On top left, click on 3 lines to open menu section 

3. Go to Accounts & Settings 

4. Go on 'Manage UPI Accounts' 

5. Then go on 'Manage bank accounts' 

6. You will find an option of changing MPIN just below the linked bank account. Click on it and chose 'Reset MPIN' or 'Change MPIN' option as per your requirement