asp.net-mvc-4 - subraction in mvc 4 from only 1 field of table

Question

I want to do subtract "1" from table bookinfo's field available

[HttpPost]
public ActionResult issuebook(string type, string accessionno, string bookname, string issuedate, string duedate, string id)
{
    tblIssuedbook issuebook = new tblIssuedbook();
    issuebook.AccessionNo = accessionno;
    issuebook.Name = bookname;
    issuebook.IssueDate = issuedate;
    issuebook.DueDate = duedate;
    issuebook.Type = type;
    issuebook.MemberId = id;
    db.tblIssuedbooks.Add(issuebook);
    db.SaveChanges();
    Bookinfo b = new Bookinfo();
    return view();
}

I want when these field are saved in the db to subtract "1" from another table according to the accessionNo