Set the date of the last commit to the current date
GIT_COMMITTER_DATE="$(date)" git commit --amend --no-edit --date "$(date)"
Set the date of the last commit to an arbitrary date
GIT_COMMITTER_DATE="Tue 16 Jul 2019 12:00:11 HKT" git commit --amend --no-edit --date "Tue 16 Jul 2019 12:00:11 HKT"
Set the date of an arbitrary commit to an arbitrary or current date