To reopen a project, it is basically the same process of closing a project - it needs to be re-submitted by sign off authority.
Go to the close object and click button "Re-submit for sign off'. Approval status changes to 'Re-Apply'.
Select the sign off Authority who will approve the opening of the project - add to the table.
Click on 'Submit for sign off' to re-submit it. Email should go to the person to approve this. Approval Status changes to 'Pending Approval'.
User goes in and clicks 'Resubmit' to Approve the opening of the project. (Note: you can relabel this to 'Reopen' or something so it makes a bit more sense to the end user rather than 'Resubmit' which is confusing actually).
Project should be re-opened and Status of the close object = Deferred.
...