Put the git-prune-local script on your PATH: git prune-local

git-prune-local

#!/bin/sh

. "$(git --exec-path)/git-sh-setup"

USAGE=""
_prune_local() {
  if [ $# = 0 ]; then
    # git 2.21+
    # -D is aggressive, beware
    git fetch -p && git branch -vv | awk '/: gone]/{print $1}' | xargs git branch -D
    # more lenient version, depends on your workflow
    # git fetch -p && git branch -vv --merged | awk '/: gone]/{print $1}' | xargs git branch -d
  else
    usage
  fi
}

_prune_local