There's no easy fix when it comes to airbag light. You will need airbag reset tool. If the fault is there, it will light up again anyway.
Sorry to hear about your bad experience. Did you have the maintenance history on the X5 when you bought it? What has been done?

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00 E39 DINAN S1 //M5 (82k miles)
06 E53 DINAN 4.8iS, born 2/18/2006 (126k miles) http://www.xoutpost.com/bmw-sav-foru...s-my-dslr.html
90 Straman Z32 TwinTurbo Convertible, (1 of 44 ever made) 5 speed, 444rwhp/451rwtq
01 360 Novitec Spider F1 (26k miles)