If the unit is still under warranty, support may be able to replace your fan if it failed (under normal circumstances). If the fan was damaged during transport or went missing for whatever reason, you may have to call Dell spare parts. The number for Dell spare parts depends on which country you're in. 
Hello all, Where can I acquire an PE T620 Cooling-Fan Assembly / Redundant Fan Option, item # 331-5673? It's not listed on Dell Parts & Accessories.  Thanks.
PE T620 - Cooling-Fan Assembly