Hi Zakaria Douiri,
No, there isn't a way to update the existing layer.
Depending on what type of results you are looking for, you could use the Append tool to append a new result to the existing one. Another potential workflow is using the ArcGIS API for Python to automate deletion of the existing layer before rerunning analysis - but you won't be able to maintain your feature service URL or portal ID - but could update with the new one using the ArcGIS API for Python.
We are looking into ways to support this updating an existing layer in the future. For this workflow, is it important that the portal item is the same as before, the feature service URL, or both?
Product Engineer, GeoAnalytics