Hi,
I followed the steps below to save my changes in CRM directly from excel online, and it succeeded.
1. Go to My Case view.
2. From the ribbon, select Export –> Open in Excel Online.

3. The data will open in excel online. Make necessary changes to the data. Here for an example, I am updating the “Origin” values for the Case.
4. After making all the changes, the interesting part is we can save the changes back in CRM. We have a button at the top ‘Save changes to CRM”

4. Once clicked, in the background CRM creates a data import job. It might take some time before the data is refreshed in CRM. So I come back in the CRM grid, click "Refresh", and find my data has been refreshed.

Note: Please keep in mind, after you do this, you need to refresh your web page.
Hope it helps.
BR,
Judy
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Appreciate to Mark it as Answer if it helps.