It is currently not possible to update items via the webform. It is a great idea though - I have moved your question to the "Feature Requests" section so other people can vote for your idea :)
You can update the item manually - and fast if you hit "e" on your keyboard to edit.
You can update the item via excel import:
And via the developers API: https://developers.podio.com/
You can also update via drag and drop using the card layout: https://help.podio.com/hc/en-us/articles/201019758-App-layouts
Sara - Podio