How do I "un-revert" a reverted Git commit?

If you haven't pushed that change yet, git reset --hard HEAD^

Otherwise, reverting the revert is perfectly fine.

Another way is to git checkout HEAD^^ -- . and then git add -A && git commit.

A revert commit is just like any other commit in git. Meaning, you can revert it, as in:

git revert 648d7d808bc1bca6dbf72d93bf3da7c65a9bd746

That obviously only makes sense once the changes were pushed, and especially when you can't force push onto the destination branch (which is a good idea for your master branch). If the change has not been pushed, just do cherry-pick, revert or simply remove the revert commit as per other posts.

In our team, we have a rule to use a revert on Revert commits that were committed in the main branch, primarily to keep the history clean, so that you can see which commit reverts what:

     7963f4b2a9d    Revert "Revert "OD-9033 parallel reporting configuration"
     "This reverts commit a0e5e86d3b66cf206ae98a9c989f649eeba7965f.
                    ...
     a0e5e86d3b6    Revert "OD-9055 paralel reporting configuration"
     This reverts commit 648d7d808bc1bca6dbf72d93bf3da7c65a9bd746.
                ...
     Merge pull request parallel_reporting_dbs to master* commit 
    '648d7d808bc1bca6dbf72d93bf3da7c65a9bd746'

This way, you can trace the history and figure out the whole story, and even those without the knowledge of the legacy could work it out for themselves. Whereas, if you cherry-pick or rebase stuff, this valuable information is lost (unless you include it in the comment).

Obviously, if a commit reverted and re-reverted more than once that becomes quite messy.

git cherry-pick <original commit sha>
Will make a copy of the original commit, essentially re-applying the commit

Reverting the revert will do the same thing, with a messier commit message:
git revert <commit sha of the revert>

Either of these ways will allow you to git push without overwriting history, because it creates a new commit after the revert.
When typing the commit sha, you typically only need the first 5 or 6 characters:
git cherry-pick 6bfabc