Very little.
Advair contains two active ingredients; an inhaled corticosteroid and a long-acting beta agonist (which helps relax the smooth muscles in the bronchi).
The beta agonist would probably provide a small measure of relief for the asthma attack but isn't really recommended for use in that situation because it's not meant to be a fast acting treatment (it tenRAB to take effect more slowly and is effective for up to 12 hours).
The inhaled corticosteroid won't do anything to help relieve the asthma attack.
Taking Advair during an asthma attack won't do any harm, it just won't do much good either (a fast acting, short-duration beta agonist like albuterol would be much more effective in relieving the symptoms of an asthma attack).
