With this error message Gerrit rejects to push a commit if the pushed commit was already successfully pushed to Gerrit. In this case there is no new change and consequently there is nothing to do for Gerrit.
If your push is failing with this error message, you normally don’t have to do anything since the commit was already successfully pushed. Still this error message may sometimes come as a surprise if you expected a new commit to be pushed. In this case you should verify that:
your changes were successfully committed locally (otherwise there is no new commit which can be pushed)
you are pushing the correct commit (e.g. if you are pushing HEAD make sure you have locally checked out the correct branch)
If you are sure you are pushing the correct commit and you are still getting the "no new changes" error unexpectedly you can take the commit ID and search for the corresponding change in Gerrit. To do this simply paste the commit ID in the Gerrit WebUI into the search field. Details about how to search in Gerrit are explained here.
Please note that each commit can really be pushed only once. This means:
you cannot push a commit again even if the change for which the commit was pushed before was abandoned (but you may restore the abandoned change)
you cannot reset a change to an old patch set by pushing the old commit for this change again
if a commit was pushed to one branch you cannot push this commit to another branch
if a commit was pushed directly to a branch (without going through code review) you cannot push this commit once again for code review (please note that in this case searching by the commit ID in the Gerrit WebUI will not find any change)
If you need to re-push a commit you may rewrite this commit by amending it or doing an interactive git rebase. By rewriting the commit you actually create a new commit (with a new commit ID) which can then be pushed to Gerrit. If the old commit contains a Change-Id in the commit message you also need to replace it with a new Change-Id (case 1. and 3. above), otherwise the push will fail with another error message.
Part of Gerrit Error Messages