I am using a neckband. And it irritates me when it reached 20% battery life by saying low battery. How can I remove that indication by changing my firmware of the neckband.

 

Not likely you can do that. Besides, we have no idea of what device you are talking about, no one can give advice without knowing what make/model it is....

 

In the realm of consumer products, I'm not aware of anyone who makes a device with user modifiable firmware. IMHO that would be an unimaginable rabbit hole of litigation, legal difficulties, and complaints. It seems you are well and truly hosed.