Closely look if it contain dust in it speaker grill/mesh. If it has dust, clean it with CTC Cleaner (you can either do it by yourself) or just ask any repair shop, he will clean it for free using brush. If there's no dust and you're facing low volume then there could be 2 possibilities
1) if volume was lower since start when you bought device, then it cannot be fixed, it is made with low volume ear speaker.
2) If you're getting low volume these days only and previously it was working good, then there could be chances that your ear speaker is faulty, it will be replaced by repairing shop / service center.
