Yes, you can.
Follow these steps to set a default assignee:
- Click the User Menu on the top right corner of the screen.
- Click the Settings button.
- Select Customer Portal under Configuration.
- Select a user from the Default Assignee drop-down.
- Click Save.
For all the cases created through the customer portal, the Assigned To
field is set to the user selected under the Default Assignee
To learn more about configuring the customer portal, click here