You should use a build-release system like VSTS. Try creating an ARM template of your app and deploy this pipeline with VSTS. You can add value to the template.json file like here:
"appSettings": [
// other entries
{
"name": "MyValue",
"value": "[parameters('myValue')]"
}
You'll require parameters.json which will hold the values:
{
"$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentParameters.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"name": {},
"storageName": {},
"location": {},
"subscriptionId": {}
}
}
And change the values of these parameters in VSTS portal.
![override parameters](https://i.stack.imgur.com/fuwzg.png)
This way you'll be able to implement a CI/CD pipeline used by professional sys admins.