Hi,
Step-1
I login to Microsoft graph using URL: Graph Explorer | Try Microsoft Graph APIs - Microsoft Graph
Step-2
There I created a custom attribute as shown in the image.

Method: Post
Version: Beta
Run query: https://graph.microsoft.com/beta/admin/people/profileCardProperties
Request Body:
{
"directoryPropertyName": "CustomAttribute1","annotations": [{"displayName": "Workstation ID","localizations": []}]}
As a Response it showed success and created Custom attribute in profile card as shown in the Image.
Step-3
Now, I want to update workstation ID for All user. How can I do that?
Please guide me on this.
Thanks.