This patient has sialolithiasis. Stones easily form here as the duct opens upwards and sludging can occur. Parotid stones are less common.
Treatment consists of manually removing the stone with forceps if it is visible.
Otherwise, prescribe something sour, such as lemon drops to try to force it out. Referral to an ENT doctor is needed as they may need to remove it. Prophylactic antibiotics are suggested to avoid infection of the blocked gland.