This TV is so frustrating!!! I am having the same problem. I try to switch back and forth from cable to fire stick with my PROGRAMED Direct TV remote and it gets stuck on VIZIO smartcast. Won't let me change the input!!! It takes me 15-20 minutes to try and get it back to hdmi1 And....it's mounted to the wall, so I can't find the model/serial number to purchase a new remote...
I just tried this because I had the same problem. Press menu, go over to setup and down to where it says source, from there you should be able to toggle to HDMI.
This worked for me.