@h3felix I confirm that I can see the appropriate TXT record.
You’ll need to wait until one of Netlify’s staff manually remove it from the other account (@Melvin @sid.m)
Give this feature suggestion a ‘like’ if you believe this should have been ‘self-service’:
https://answers.netlify.com/t/fix-another-site-is-already-using-this-domain-self-service/46443