I created a branch from Master using git checkout -b mybranch. After modifying some files I wanted to commit but couldn't because of some error. After reading some posts I deleted the git index (rm .git/index) and was able to commit afterwards. However, now I see that the files I did not modify are missing and are not in the index anymore, whereas the files I modified are there. I can't Add the missing files to the index; the Add option is greyed out (in IntelliJ). But I also want to do more than just add the missing files: I want to fix that original commit. How can I do that?
Update: I don't know enough Git to know that this is the same a moving "Head" back; hence the question. I think it will be useful to complete Git newbies like myself. Thank you for pointing out that this is effectively what I need to do.