Dynamically update an entry from zapier


I am wondering how I can accomplish the following: Update an entry after it has been submitted from an external source.

Here is my use case:

user input information
information is submitted and sent to zapier to have the url shortened
after the url is shortened, the new url is sent back to the record to be stored in a different field

I am not sure how to get this done…

any help would be greatly appreciated.