It sounds like you're using some kind of GUI but you haven't specified which. If you want to jump back to a previous revision, you can use the following
git checkout HEAD@{1}
This goes back to the previous revision in the git reference log. However, you will be in a detatched HEAD state. This means any commits you have will not be associated with a branch and new commits from any branch will not be automatically pulled in. This is probably not what you want.
If you know which branch you want to be on, you can use
git checkout BRANCH_NAME
Alternatively, if you know you were on some branch but not sure which one, you should be able to get the name of the branch with
git name-rev $(git reflog --pretty='format:%H' -1)