To get back to that commit you can use the reflog to look up it's ref.
Reference logs, or "reflogs", record when the tips of branches and
other references were updated in the local repository.
Run this command:
git reflog
Scan the first few entries, and find the commit that was lost. Keep track of the identifier to that commit (you can use either the 1st or 2nd columns). Let's call the identifier "ID".
If you have not made any extra work since you did the reset --hard you can do:
git reset --hard ID
git push -f origin master
If you have made other work since the reset, you could cherry-pick if back onto your branch like this: