All TVs have a power button. Manufacturers are getting better and better at hiding it. If it's not on the back, it's usually on the bottom near the manufacturer's logo or IR sensor for the remote.
Cancelling Spectrum shouldn't have anything to do with your TV connecting to your Wi-Fi. If your TV is near your router and if it has an Ethernet jack on the back you may be able to connect the two with an Ethernet cable and then maybe the app will find it and you can figure out what happened with Wi-Fi. Did Spectrum change any of your network equipment when you cancelled?
One thing to try - disconnect the power to the TV for a few seconds and then reconnect it to get it to restart.
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