@J, Munna Lal Thank you for reaching out to us, steps in this mentioned article https://learn.microsoft.com/en-us/azure/role-based-access-control/role-assignments-powershell steps have been defined in how to assign roles using Azure PowerShell
Reference: https://www.easy365manager.com/azure-rbac-roles/
Would suggest you to follow these steps, if in case you come across any issues let me know.