Podio shows you how to do it here:
Basically we need to collect the users email or ID (up to you) and then add it to the webform URL.
You can either use a calculation field to show a clickable link or image which opens a new tab with the webform.
Here are two examples, one for image and one for text link.
Then add your calc field in the Portal settings, you can turn on the calc resolver to make sure it is always updated and not relying on calculations being done in Podio.
Set up the webform in Podio to redirect back to your Portals URL to have the user being returned to your Portal after submitting the form.