By default the git commands that require an editor would use ‘vi’, but if you can add an entry into your global git config to change the editor to Notepad++. To change to some other editor such as Notepad++ or Textpad you can add these lines to the global git config. For example:
[core] editor = '/C/Program Files (x86)/Notepad++/notepad++.exe' -multiInst -notabbar -nosession -noPlugin
[core] editor = '/C/Program Files (x86)/TextPad 5/TextPad.exe' -m
Either edit the global config manually or you can run this git command
git config --global core.editor '/D/ProgramFiles/Notepad++/notepad++.exe -multiInst -notabbar -nosession -noPlugin'
NOTE: If your editor path contains spaces you could have trouble running the above git command. Recommend to just edit the global config directly in that case to ensure the editor gets added correctly.