If you have a branch like this
Master
  7243798 M
  60789fc M
  4c629bb M

And you push 6bbw138 commit by mistake to Master your result will be:
Master
  6bbw138
  7243798 M
  60789fc M
  4c629bb M

  If you want to come back to 7243798 or previous

  1) on local repo go to your master branch:
  git checkout master
  2) Then we need the commit id to do a a reset of master branch in our case 7243798
  git reset --hard 7243798
  3) We need to push this change to our branch, in our case is master branch
  git push origin master -f

 I used bitbucket repo, this will be the output

Total 0 (delta 0), reused 0 (delta 0)
To bitbucket.org:square1/www.myrepo.test.git
 + 6bbw138...7243798 master -> master (forced update)

 And that's it you will have your branch on the previous commit.

 Master
  7243798 M
  60789fc M
  4c629bb M