If you are referring to the 'Convert Request to a Project' App from the Apps Marketplace, this runs on the Request Item Type so you do not need to specify CurrentObject, you can do the following...
1 - Add an Action using the Update option
2 - Click on Select Field to specify the field you want to update (this will say Change... if you already set).
3 - select State as the field and click OK
4 - Specify the following as the updated value: 'Approved'
(with single quotes)