How to reset an empty merge commit

Hi All,
How to revert an empty merge commit ?

scenario: one of my colleague is having very old copy of dev branch [5 months old] and accidently he merged it into our new dev. Now all files in my dev branch are showing 5 month back changes. how to revert it and get my dev back as updated copy.

You can use git reset <COMMIT> to reset the branch to a specific commit. You can then force-push the fix to a shared repository, but double-check first to make sure you’re not deleting anything that should be kept. :warning: