A few months back I purchased a couple Echo Dot's to start some home automation routines. I found the Roku skill and enabled it and setup my 55in TCL as the default TV to control. Now time has passed a bit and now the 55in TCL is losing favor in quality and I would like to change the ability to control another device. like my 32in TCL that is in the bedroom.
You can change this in the Roku SKILL that is enabled in the Alexa app installed on your mobile device.
Open the skill in the Alexa app and select SETTINGS and then MANAGE IN TV & VIDEO and you should have a screen that will DISCOVER DEVICES and you can then select individual Roku devices and LINK them to a specific ECHO Dot.
FYI. A recent update to the Roku SKILL allows you to control multiple Roku devices from any of your Echo speakers. Linking a specific Echo to a Roku device will default to it for voice commands, but you can issue voice commands from any Echo speaker to any Roku device as long as you use the specific name that it is set up as in your Roku account and what displays in the SKILL under SETTINGS (i.e. Living Room Roku, Bedroom Roku, Kitchen Roku etc.)
TCL Roku-TV 55P605 (4K/HDR/DV) | VIZIO SB36512‑F6 ATMOS Soundbar | Fire TV Stick 4K TCL Roku-TV 43S425 (4K HDR) | Fire TV Stick 4K TCL Roku-TV 32S301 (720p) | Fire TV Stick 4K YABER Y31 1080p LED Projector | ONN 5.1.2 Dolby ATMOS Soundbar | Fire TV Stick 4K