I have a project with a Git submodule. It is from an ssh://... URL, and is on commit A. Commit B has been pushed to that URL, and I want the submodule to retrieve the commit
If you don't know the host branch, make this:
git submodule foreach git pull origin $(git rev-parse --abbrev-ref HEAD)
It will get a branch of the main Git repository and then for each submodule will make a pull of the same branch.