Let us see how to add tasks to VSTS from Excel.Instead of adding it from Azure Boards it’s easier to add it via Excel
Step 1: Open Excel and Click on Team tab (By Default it’s available in latest version of excel)
Step 2: Click on New List on the team tab as shown

Step 3: If there is no AzureDevops(VSTS) server saved, a popup would be displayed as shown below, Click on servers in the popup

Step 4: Click on Add Server as shown

Step 5: Then Add the Azure Devops (VSTS) url as shown below

Step 6: Then Enter the username and password as shown

Step 7 : Once you have signed in, the VSTS url will be displayed as shown

Step 8 : Then select the Project for which you want to add tasks as shown
Step 9 : Then select the Query as shown (A simple query can be directly created from Backlogs)

Step 10 : You will see some thing like this in the Excel sheet

Step 11: Add as shown in the below excel and then click on Publish button.Once published you can see workitem ids next to it

You can see on it Azure Boards also