try it

.github/workflows/scalafmt.yml

@@ -2,12 +2,17 @@ name: 'Scalafmt'
 
 # This GitHub Action runs the ScalaFmt linting tool on the entire codebase.
 # It fails if any files are not formatted properly.
+# If it is triggered by someone commenting 'scalafmt' on a PR, it will first format, commit, and push formatted code
+# to the branch.
 
 run-name: ${{ format('Scalafmt on {0}', github.ref_name) }}
 
 on:
   workflow_dispatch:
   push:
+  issue_comment:
+    types:
+      - created
 
 permissions:
   contents: read
@@ -23,6 +28,26 @@ jobs:
       - uses: ./.github/set_up_cromwell_action
         with:
           cromwell_repo_token: ${{ secrets.BROADBOT_GITHUB_TOKEN }}
+      - name: Check for ScalaFmt Comment
+        run: |
+          if [[ "${{ github.event_name }}" == "issue_comment" && "${{ github.event.comment.body }}" == *"scalafmt"* ]]; then
+            echo "::set-output name=comment-triggered::true"
+            echo "::set-output name=comment-author-email::${{ github.event.comment.user.login }}@users.noreply.github.com"
+            echo "::set-output name=comment-author-name::${{ github.event.comment.user.login }}"
+          else
+            echo "::set-output name=comment-triggered::false"
+          fi
+        shell: bash
       - name: Run ScalaFmt
         run: |
+          if [[ ${{ steps.check-comment.outputs.comment-triggered }} == 'true' ]]; then
+            echo "PR Comment Detected. Formatting, committing, and pushing formatted scala code.
+            sbt scalaFmtAll
+            git config --global user.email "${{ steps.check-comment.outputs.comment-author-email }}"
+            git config --global user.name "${{ steps.check-comment.outputs.comment-author-name }}"
+            git add .
+            git commit -m "Auto-format code with ScalaFmt"
+            git push origin ${{ github.ref }}
+          fi
           sbt scalafmtCheckAll
+        working-directory: ${{ github.workspace }}