What procedure can remove a 5.5mm stone from sub salivary gland or the gland has to be removed?

Surgical removal. The stone can usually be removed surgically without removing the gland itself, but not in 100% of the cases.
Ultrasound. I would go to a physician and see who they would recommend to remove the stone using ultra sound. Ssound waves produce a vibration that tends to break up the stones good luck!