Set the Assigned To field to the Current User for Cases created in the User Interface using a Workflow

To create the workflow:

1. Navigate to  Customization > Scripting > Workflows > New.
2. In the Basic Information section, set the following:

• Name: For example, "Set Assigned To = Current User"

• Record Type: Case

• Execute as Admin is checked

• Release Status: Released
    

3. In the Initiation section, set the following:

• Event Based: On Create

• Trigger Type: All

4. Click Save.
5. Click State 1.
6. Update the Name and set a descriptive label, then click Save.
7. Click the first State  > New Action.
8. Click Set Field Value.
9. In the Basic Information section, set the following:

• Trigger On = Entry

• Event Type = Create

• Context = User Interface

10. In the Parameters section, select Assigned in the Field dropdown.
11. In the Value section, set the following:

• Static Value = T

• Selection = Current User

12. Click Save.