Thanks for the inquiry.
If you are trying to activate the HGTV GO channel, when you go to the channel and sign in, it should request you to activate the device as the channel is free with a paid cable subscription and participating TV providers. It should prompt you to go to: https://watch.hgtv.com/activate on a computer or a mobile device where you will enter the activation code and continue with the activation process.
If you are having further issues activating the HGTV GO channel, we would recommend reaching to the channel provider's support directly to inquire further. Many channels on Roku are developed and maintained by the channel provider themselves.
You can reach HGTV support here.
Roku Community Moderator