[요약]
[Win] C:\Users\USERNAME\AppData\Local\Atlassian\SourceTree 폴더의 passwd, userhosts 파일 삭제
[OSX] Home(Shift+Command+H)/Library/Application Support/SourceTree 폴더의 userid@STAuth-xxxxxx 파일 삭제
Library 안보이면 Home에서 Shift + Command + . (http://macnews.tistory.com/5286)
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The only thing that worked for me was navigating to C:\Users\USERNAME\AppData\Local\Atlassian\SourceTree and removing the passwd file.
Once this file is removed, restart SourceTree and execute a fetch or something else that requires access to the repo in question. SourceTree will then prompt you for your password, rewriting the cached credentials.
I hope this helps. Shoutout to my buddy Nick for the assist.
If you're a macOS user, Auke states below that "you can find the password files per repo it in ~/Library/Application Support/SourceTree"
[출처]
https://community.atlassian.com/t5/Sourcetree-questions/How-to-update-HTTP-S-credentials-in-sourcetree/qaq-p/297564
[참조]
https://igotit.tistory.com/entry/Git-SourceTree-%EC%9B%90%EA%B2%A9%EC%A0%80%EC%9E%A5%EC%86%8C-%EB%B9%84%EB%B2%88-%EC%A0%80%EC%9E%A5%EB%90%9C%EA%B2%83-%EC%82%AD%EC%A0%9C%ED%95%98%EA%B8%B0