have adsense for my blog already, how do i link my youtube channel?

worked for me the same way. one thing that caught me out: the AdSense account doesn't have to be on the same google login as the channel, you just sign in with the AdSense one at that step. so don't move your channel or make a new account to match. youtube earnings then show up alongside the blog ones and pay out together.

You link it as part of applying to the YouTube Partner Program, from the Earn section in YouTube Studio. When it asks for AdSense, pick the option to use an existing account and sign in with the Google account that owns your blog's AdSense. Don't create a second AdSense account, you're only allowed one and a duplicate gets rejected. You can't link it before the channel meets the partner program requirements, so if Earn isn't letting you apply yet, that's why.