GitHub makes it difficult to create PRs for forks, and IIRC the plugin is quite different from the source (raymond-w-ko/detectindent) already?!
When doing this, it might be good to also rename it to have "vim" in the name, "vim-detectindent".
I think you need to contact the support to remove the "fork link".
You could also create a new repo, but then you do not get redirects!