SHELL

git revert merge

git revert -m 1 <merge-commit>

how to revert a merge locally

git reset --hard <cbm>

where cbm is the commit number before the merge you want to revert
to get a list of all the merges you can use the following line

git log --graph

and then use the commit number from the one before the merge you want to revert

revert local merge

git reset --merge origin/master

how to undo a merge in git

git reset --merge a9fdeb5