Change date format to build http redirection query

I want to apply a dd%2Fmm%2Fyyyy format, neither in web form nor in email template, but very important into the url string parameters sent, created once press send buttom.

My field is built like this

[date departureDate min:2020-07-01 max:2020-07-31]

BUT I need send an string while redirection to convert to:

http://www.example.com/?departureDate=31%2F04%2F2020

To internally let this external website works.

Thanks in advance.