choose the newly exposed link “link to another repository”
but actually link to the same one.
If that doesn’t work, I’d check the settings at GH to see if the app was approved for use in your account. I can’t send you to a direct page, but you should be able to click “configure” from this page on the netlify app (or approve if it shows waiting for approval):
…and send me this screenshot from your settings page for our app: