Updating git config file after migration

Question

I need to migrate from a self-hosted GitLab instance, into GitHub. I have searched and would like to try the mirror method:

git remote add github https://[email protected]/yourLogin/yourRepoName.git
git push --mirror github

I did that and see the files and history on GitHub. Now, I am getting ready to decommission my GitLab server and I assume I need to remove the remote associated with it. This ought to work:

git remote rm origin
git remote rename github origin

When I do that, my config file get's messed up:

PS C:> git push origin

fatal: The current branch master has no upstream branch.

To push the current branch and set the remote as upstream, use

git push --set-upstream origin master

I tried that, then made a change, staged, and pushed it, but it did not go to GitHub or GitLab (though git push origin says, "Everything up-to-date") and the status still shows I have a modified file.

For reference, my config file says:

[core]
    repositoryformatversion = 0     
    filemode = false
    bare = false
    logallrefupdates = true
    symlinks = false
    ignorecase = true
[remote "origin"]
    url = [email protected]:myOrg/myRepo.git
    fetch = +refs/heads/*:refs/remotes/origin/*
[branch "master"]
    remote = origin
    merge = refs/heads/master

Not sure where I go from here.