You can easily turn subtitles on or off by pressing the [SUB] button on your remote control. Or if you have the TV Box Pro, press the MORE button (top right hand button with three horizontal lines on) and then go to the Subtitles menu.
Alternatively, press the main menu button then go to Settings > Accessibility & Language > Language & Subtitles. Select your preferred setting and go to Done.
Subtitled programmes have an [S] icon next to their title in the programme guide.