I keep this script around which lets me apply a git command to every subdirectory:

git-alldirs.sh

#!/usr/bin/env zsh

submodules=("${(@f)$(find . -type d -depth 1)}")
for submodule in $submodules
do
    print "=== $submodule"
    git --work-tree=$submodule --git-dir=$submodule/.git $*
    print
done

https://stackoverflow.com/a/48153471/855050