git merge with message
$ git merge other-branch -m "Commit Message"
Source: stackoverflow.com
after git merge it want to commit message
press "i" (i for insert) write your merge message. press "esc" (escape) write ":wq" (write & quit) then press enter.
git edit merge commit message
For current Git versions (2020+), just do git rebase -i -r <parent>, then replace in the editor merge -C with merge -c. This will open the merge commit's message in the editor during rebasing, where you can change it
Source: stackoverflow.com