Hi @Rumaysa ,
have you been able to connect these using this app before?
Have you registered the TV to the SmartThings app on your phone via the Add Device feature on the home page? If so, if you head to Home > SmartThings > Device List on your TV, is it showing up?
Have you tried any of these solutions;
Restart the application;
Are all these devices connected to a same wifi network, if not then make sure all are connected to the same wifi
Reboot your Router
I was also facing the same issue while I was trying to download Google Chrome on Samsung Smart TV, but these steps helped me