Hi @Proimobi-8218,
just to add to Leno's response, the latest version of .NET core is v2.1.19. you can find it here
Run the following command in the Cloud Shell to set the .NET Core version to 2.1:
az webapp config set --name <app-name> --resource-group <resource-group-name> --linux-fx-version "DOTNETCORE|2.1
I hope that helps. Let us know if you have further questions.
Thanks, Grace