You won’t need to open a brand-new AdSense account—your existing one can stay active—but you can only hook it up to a YouTube channel that’s been legitimately approved for the YouTube Partner Program. If you buy a “monetized” channel off someone else, you run a few big risks: YouTube could flag that channel’s history and kill its monetization (which can then cascade into an AdSense suspension), and you’re also running afoul of their Terms of Service around account transfers.
A far safer path is to create your own fresh channel, build it up according to YouTube’s rules (original content, no policy strikes, minimum subscriber/watch-time thresholds), and then reapply for monetization. Once that new channel gets accepted, you simply point your existing AdSense account at it under YouTube Studio → Monetization → AdSense Account. That way you keep all your earnings history intact and avoid the headache of buying someone else’s channel data (and the potential for a re-suspension that could also take your AdSense down).
