im trying to create a button that deletes a record how can i do that?

Why? The delete button is already there.

because i want to delete item fulfillments only when status is picked

You probably don't need a button for that but a validation check.

A custom workflow action script that just does record.delete would do it. You could have it trigger based on a button and run as admin. Then you could make the native delete be not needed.

@Zack thats exactly what i did but im getting an error. Can you help me out. Here is the error: Cannot read property "type" from undefined

You could have hidden the delete button unless the criteria was met, might have been simpler to do in a UE script.