ATT app disappeared on Samsung tv

Could you be more specific about what you mean by "The app for ATT UVerse"?  Because AT&T's U-verse App had spotty availability on TV platforms, and is totally unnecessary if you have a receiver (as you indicate). 

I'm thinking maybe you mean the HDMI input from the receiver has disappeared from your selection list?

JefferMC

On the Home Screen of my Samsung TV there was an icon that showed “ATT UVerse.  I would just click on it to use UVerse    Now the icon has disappeared and no one can tell me how to get it back at Samsung, or ATT support line. All 3 of my other TVs work fine. The support line did say UVerse is not being supported  as much, but they sure like me to keep paying my bill.    Any help is appreciated!!

Charlie

And when you clicked on it, it essentially switched your TV's input to the one connected to the U-verse Receiver, right?  

Apparently someone who liked you (or maybe a U-verse Premise tech who liked doing a good job... or both), created a named for the input connected to the U-verse TV receiver, as described in the link below:

https://www.samsung.com/sg/support/tv-audio-video/how-to-switch-between-external-devices-connected-to-samsung-2018-qled-tv/

It might be that the receiver isn't putting out any signal, so the input icon isn't showing.  Unplug the TV receiver from power and plug it back in, wait a few minutes and see if that brings it back.  Also, check to make sure the cable from the TV receiver to the TV itself is well seated on both ends.  

If doing that doesn't bring it back, I'd switch one of the other non-DVR TV Receivers from one of your other TVs and see if the problem moves to the other TV.  You may have to also swap the power supplies (because the power supplies can often go south while the box itself is fine).