Sending Grades from Markbook to Existing Assignment on Google Classroom

Hoping someone can help... Here's my issue:
- I create an essay assignment on Google Classroom.
- Students submit their work (essay) on Google Classroom.
- I add the assignment to my Gradebook on iDoceo (new column) and create a rubric for it
-I mark the essays using the rubric on iDoceo
**I want to send the marks back to Google Classroom so that they appear with the original assignment I created. But if I try to send the marks to G.C., it creates a NEW assignment. I can't see a way to just send the marks to the existing assignment.

Is this not possible? If so, can someone tell me how?

Thanks!

* To be clear, I want to send the marks AND the rubric back to Google Classroom

Hello.
It is a limitation on Google's side.
If you create the assignment in Google, no other app can write grades on it.