You can't. Subscriptions made through Roku can only be accessed on Roku devices. If you need access from a non-Roku device, you need to cancel your subscription through Roku and subscribe directly with the provider. You then use the credentials you have with the provider to log into their app/channel on any device.
The Roku Channel app on other devices only provides access to The Roku Channel. To access any other content you have to use the app designed for that provider.
I suspected as much but I thought I would ask
rms5366, for Peacock, try logging in on the Peacock website using the email address displayed under Settings->System->About on your Roku device. There should be a "forgot password" link. Click it and you should get a password reset email from Peacock. Once you establish a password you should be able to use the email address and password anywhere. I gave these instructions to a family member not too long ago and it worked for them.
Good luck!
