@AnalystRAC This support page might help you: Date Field Format (CX) (qualtrics.com)

Thanks @dxconnamnguyen for your reply. Customising date format is good but unfortunately it doesn’t work for transaction date in ISO-8601 format. 

If the transaction date in ISO-8601 format is being accurately picked up during distribution but appears blank in the Data & Analysis tab as well as the dashboard, there might be a formatting or mapping issue.
check for field mapping or date format settings

also have a look at the dashboard Configuration or Check if there are any filters or settings in the Data & Analysis tab that might be causing the transaction date to appear blank. Make sure the date field is selected for analysis.

Below is the response I received from Qualtrics Support, however, it doesn’t solve my problem. 

“You would have had to setup the respondent funnel before you started collecting responses.

If you are not able to give up the data, unfortunately you will have to manually update the data.”