There is not much to go on here…
Has this TV recently worked with Plex?
Hisense has limited support, like most Smart TV.
Some reference for you to consider.
https://support.plex.tv/articles/204080173-which-smart-tv-models-are-supported/
If your Tv is not supported, your best bet is to purchase a third party device, like Roku, Apple TV or alike.
