@Sallybui123 

Hello, from your descirption, the pc can get internet from the extender, that means the TL-WA855RE should be working well; we can do some troubleshooting first. 

1. With TV connected to the main router by wired cable directly, does it work？ And is there any other settings have been done on the main router to make it work? Like port forwarding or VLAN?

2. With TV connected to the extender, please check its IP address and gateway; 

3. Besides, you can give a call to the TV tech support to get some suggestion cause they are more professional about their own devices. 

Good day.