I've added bridges and power lines to the existing network through the Rest API web service. But new lines and bridges are not capable of Set Flow and must be manually connected using ArcGis tools to allow Set Flow. I want to know how it is possible to perform Set flow through Web service Arcgis?
I assume this is what you're looking at in terms of Set Flow?
It is not avaliable by default as a REST api, but you could create a Geoprocessing tool that executes the single "Set Flow" command you need and publish your geoprocessing tool to your Portal environment. That would create a REST url to be able to access your geoprocessing tool (which you would set up as the Set Flow tool).