
Hi @david_castillo,
What is your external source? Learn how to create custom connectors for canvas apps here:
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/register-custom-api
If you could create the custom connector, then this could be achieved by using Patch function to update records to SharePoint list connection.
The formula to update records to SharePoint list should be something like below:
Patch(ListName,Defaults(ListName),{Title:Label1.Text, Choice: Dropdown1.Selected,...})
Regards,
Mona