if the update operation is already connected to the input port through an Ok Flow all you have to do is to bind by hand the value 'true' for the finished attribute (yes, you can write directly into the parameter binding dialog to use static values).
- true all lowercase is the string equivalent to the true boolean value
- false all lowercase is the string equivalent to the true boolean value
More generically you can submit from the form only one field instead of the whole object and bind it using the Ok Flow connecting the input port and the delete operation.
Let me know if this works.