I am using
I think you are confused "Change-Id" (Gerrit) with "Commit-Id" (Git). When you resolved the conflict and amended the original commit a new commit was generated with, of course, a new Commit-Id. You can (actually, you need) keep the same Change-Id at the commit message last line, like for example:
When you push this commit to Gerrit, it will use this line to know that this commit is an amend (new patchset) of the original one and it will add this to the original change.
See more info here.