Working with TV firmware carries a high risk of "bricking" the device. Always keep a copy of the original factory firmware and ensure you have an ISP programmer (like the RT809H) available for recovery if a flash fails.
You can find download links and detailed user manuals on Software Repair Training (OneTV-SRT) and KenotronTV , which are leading communities for MStar firmware porting. mstar bin tool guiv232 download link