In addition to @neilgallen's response, which I believe is the best solution if you want to be prompted for the date at run-time, youll want to add a Formula tool, or DateTime Tool to get the custom format you desire
In a Formula Tool, you can enter:
For the DateTime Tool, you'll want to select the "Date/Time Format to string" option at the top of the configuration, and then in the "Select the format for the new column" box, find your desired date format (dd/MM/yyyy)
When you run this, it will output a new column with the desired format of the date from your user input.
I've attached a sample app, let me know if you have any troubles with it or any questions.