Changing the last commit message
What you are wanting to do is change (rewrite) the last commit message to add the signed-off line.
Go to the git status window (a common key binding is
c to get into commit
-s to enable the signed-off line
w to reword the last commit message, check that you have the wanted signed-off field.
C-cC-c to do the commit
-s as the default
You can set the
-s option as the default by
c to go to commit
If needed, type
C-t to enable the common options
-s to toggle the signed-off, toggle other options as desired.
C-cC-c to set the defaults.