My recommendation for a permanent safe fix (as long as there is enough unchewed cable left, and you know how to wire up appliance cables, or can get an electrician/ repair person to do this for you).
Get an IEC C14 inline socket (eBay or electronic supply place). Cut cable a short way from TV, attach inline socket. (Throw away rest of chewed cable).
Buy a standard appliance/computer power cable (wall plug one end, IEC c13 on other). Plug appliance cable into c14 inline socket, plug into wall. Job done. And easy to fix again if dog chews again.
Good to be careful about live/neutral polarity across the plug (use a multimeter to test appliance cord vs. existing wire colours, would be brown live in UK but don't know US colours) but may not be too critical in this case as long as earth wire is in right place (should be obvious by colour code, green/yellow in UK, and it's the middle of the 3 connectors in the socket).
Other IEC connector styles available and may also suit, e.g. "mickey mouse" cable used on computer power bricks, or "figure 8" type if TV doesn't have an earth wire. Look up the various IEC styles on wikipedia, and check max amps permitted for style, but C13/C14 is plenty amps for a TV and may be easiest to get.
Not a Roku employee