I currently have a number of YouTube accounts. Three of them have monetization enabled. Each of the YouTube accounts is linked to a different email address.

Two of the YouTube accounts, use the same AdSense account.

I can't find any setting anywhere to get the third YouTube channel associated with the same AdSense account the first two are linked with. I've looked in the monetize tab in the 3rd YouTube accounts settings - nothing. I've also looked through the settings in the AdSense account.

It's driving me crazy - can anyone help?

Many thanks.
Adam