You have to remove the back plate and lift the screen. There’s a white backer that covers the led array. On each led there is a diffuser cap. Sounds like the glue on yours failed on one or multiple caps. While in there wiggle any of the other caps so that if the glue failed on any of them you can address it all at once. Get some glue like either gorilla glue or super clue and glue the diffuser caps back down over the diodes. This is a known issue with Samsung tvs. https://m.youtube.com/watch?v=Tv5s0KttNX0
this link shows how it’s done.