Let's assume you are using fugitive
for Git integration with Vim. You've made a commit that you want to amend.
First, stage any changes that should be included in the amend with :Gstatus or
:Ge:. Then hit ca to open up the commit window for amending. Save and
quit when you are finished.
Want to view the aggregate changes? Open the commit window for amending in
verbose mode with cva.
See the vim-fugitive docs for more details.