You need update the Fire TV at the latest software version. Different fire TV having different OS. Go to setting, my fire tv, information, and looking for new software update. Please let me know.
Here the list:
Amazon Fire TV Devices
Amazon Fire TV Cube (2nd Generation): Fire OS 7.2.4.2 (21039196292)
Amazon Fire TV Cube (1st Generation): Fire OS 6.2.8.1 (5604456836)
Fire TV Recast: Fire OS 6.2.8.1 (5604456836)
Amazon Fire TV Stick 4K: Fire OS 6.2.8.1 (5940172420)
Fire TV Stick 4K Max: Fire OS 7.2.5.5 (21911667588)
Fire TV Stick (3rd Generation): Fire OS 7.2.4.2 (21710459012)
Fire TV Stick Lite: Fire OS 7.2.4.2 (21710459012)
Amazon Fire TV (3rd Generation): Fire OS 6.2.8.1 (5604456836)
Amazon Fire TV (2nd Generation): Fire OS 5.2.8.0 (671760920)
Amazon Fire TV (1st Generation): Fire OS 5.2.7.4 (656639420)
Fire TV Stick with Alexa Voice Remote: Fire OS 5.2.8.4 (672751320)
Fire TV Stick with Voice Remote: Fire OS 5.2.8.0 (671760920)
Fire TV Stick (1st Generation): Fire OS 5.2.8.0 (671760920)
Fire TV Stick Basic Edition: Fire OS 5.2.8.0 (668694820)