In this article I will explain how one can start multiple VMs on Azure using a pipeline automation. The steps you need to follow:
First create a service connection with your subscription. You should navigate to service connections -> azure resource manager and then select service principal (automatic)

You will then have to select the scope* the subscription or resource group this service connection will access.

In my scenario I added a friendly name of the subscription as Azure Subscription Service Connection
When you run the pipeline you will need to provide the VM names. You can also run this pipeline on a schedule using a cron task. My vms are ubuntu1, windows-1

By running the pipeline

Then by navigating on Azure you can notice the VM as started.

Video tutorial on YouTube: