What you mean integrate on "all my APIs are in Azure App service and this has to integrate with Windows desktop application.". Try to explain a little bit what's your requirements.
If you want to Read/Write a SQL DB on premises, you can use a Azure Gateway without deploy anything in your server, another choice with SQL Server is to move the DB to Azure (if supported). You can use the triggers on Azure Functions to write/read something on Azure Storage, from your Server you can read the storage and perform some tasks. As you can see there are multiple choice without writing much code on premises, try to clarify your requirements.