ES notes to update guides

doc/update/8.7-to-8.8.md

@@ -151,6 +151,16 @@ When index mapping is changed the whole index should be removed and built from t
     bundle exec rake gitlab:elastic:delete_indexes
     ```
 
+1. Clear repository index status:
+
+    ```
+    # Omnibus installations
+    sudo gitlab-rake gitlab:elastic:clear_index_status
+
+    # Installations from source
+    bundle exec rake gitlab:elastic:clear_index_status
+    ```
+
 1. Create new, empty indexes:
 
     ```