Velvet upholstery is quite difficult to clean. Brush as much of the dust out as you can. I would use a soft brush like a gents shaving brush or a pastry brush. If it’s very dusty catch the brushed out dust with a vacuum cleaner nozel… don’t vacuum the velvet itself.
Make up a solution of washing up liquid and use the suds and your fingers to very gently moisten the velvet. Blot it dry with clean cloth… DO NOT RUB. Work your way over the velvet adjusting your technique as you see how it works. DON’T over wet the velvet.