Step 1: Login into portal.office365.com
Sign in with your Login ID and Password.
Step 2: When entering account click on Admin as shown into the picture.
Step 3: In the admin portal click on the User.
Then Active Users.
Step 4: Now click on the User, a window will appear then. Click on the Edit button in front of alias name option as shown in picture.
Step 5: After clicking on the Edit button now we have to enter the alias name, after entering the alias name click on the add button and the save button.
(Note: We can set the alias name as our primary id from here if we want.)
Here we can see that we successfully