The Gradle Plugin Portal doesn’t support multiple owners. Since one of your contributor’s published it with a personal account, it belongs to that account, not yours.
If you don’t want it to be a personal account, you can always create an account that represents your “organization” (even if it’s not really an organization by other definitions).
Either way, you’ll need to request a transfer if you don’t want to it to stay with the current account. You will have to share the credentials for whatever account that is if you want multiple people to publish locally, but ideally you have a CI/CD for the release process and the right people can trigger that automation without sharing the real credentials.