We encourage learners that are looking for more resources to prepare for the Digital SAT to use both Khan Academy's Official Digital SAT Prep for skill practice and College Board's Bluebook app for full-length practice tests.

I don't think there is a way to connect those accounts anymore. Why do you need them connected?

I found that here: https://support.khanacademy.org/hc/en-us/articles/17921365165581-Moving-from-Official-SAT-Practice-to-Official-Digital-SAT-Prep-on-Khan-Academy